Nouns inflect for case and number.  But nouns have gender, right?  Why didn't I check the gender box in the table? (There was a table showing which parts of speech inflect for what which I haven't reproduced in this post.) Because nouns don't inflect for gender: a noun is automatically masculine, feminine or neuter, so it doesn't need a special ending to show the gender.

Declensions

Nouns in Latin fall into five declensions, which are patterns of inflection.  There is one class of nouns which follow the First Declension pattern, another which follows the Second, and so on.  It's kind of like how there are different patters for forming the plural of English nouns.  Some add -s: door, doors; cup, cups; some add -en: ox, oxen; child, children; some change the internal vowel: mouse, mice; louse, lice; some do nothing: sheep, sheep; deer, deer.  So in the same way, Latin nouns fall into classes which dictate how they change their shape, and consequently tell you what they are doing.

How to tell what declension a noun belongs to

In order to adequately explain this, I'm first going to tell you how to read a dictionary entry for a noun.  There is a standard way words are presented in dictionaries, and you'll see this in any Latin dictionary you use.  Let's take a look:

fōrma, -ae, f. form, beauty, shape

There are four parts here.  The first is the nominative singular.  The second is the genitive singular ending.  Next comes the gender, which will be m., f., or n.  Finally we have the English definition.  The second part of the entry, the genitive singular, is what tells you the declension of the noun.  In this example we have -ae, which means that the word is First declension.  Here's a table which shows you all of them:

This is important to keep in mind..  If you don't remember what declension a noun belongs to, then you'll get confused by words like corpus, which look like they might be 2^nd declension because they seem to end in -us.  But in fact the full dictionary entry is corpus, corpōris, n. body.  So this noun belongs to the Third declension.  Don't make the mistake of writing *corpum for the accusative.  That would be wrong.  So always check the second element of an entry for the declension.  You should also “store” the entire entry in your brain.  Don't think “corpus means body,” but “corpus, corpōris, neuter.  That means body.”  Got it? Good.

PRONOUNS

Pronouns are those words which stand in place of a noun (prō + nōmina).  There are many different pronouns in Latin, each with their own special sense or shade of meaning.  Let's check them out:

ego, nōs; tū, vōs; hic, haec, hoc; ille, illa illud; iste, ista, istud; is, ea, id; īdem, eadem, idem; ipse, ipsa, ipsum; quī, quae, quod; quis, quid.  That's a lot, isn't it?  There's no way I can go into a ton of detail on each and every pronoun, so I'm just going to say a few things here. 

First and Second Person Pronouns

The first person pronoun, “I” or “we” is ego, pl.nōs.  The second person pronoun is tū, pl. vōs.  These are called “pronouns” because they are used in place of a noun or name.  I say “I” in place of “Luke”--that is, I don't refer to myself in the third person when using “I”, rather I'm using a first-person pronoun!--and I say “you” in place of “Tara.”  In English we use these pronouns all the time, but this is not the case in Latin.  Why?  Because the -ō at the end of a verb means “I _____,”  so saying “ego ______-ō is redundant.  It is actually quite rare that you will see first and second person pronouns in the nominative case,[1] but you'll see them fairly often in the other cases, e.g., tē amō, because verb endings only tell you something about the subject but not the object.  So why does Latin even bother with having ego, tū, and so on?  Two reasons:

In literature, the presence of a pronoun indicates emphasis.  One could write tē amō and get one's point across just fine, but writing ego tē amō is stronger.  It may also serve to make a contrast, as in: “Carolus mē amat.”  “Nōn!  Ego tē amō!”  Stronger still is egomet.  Another use of these pronouns is in actual speech.  Romans in everyday speech likely used them just as much as we do.  I you read Plautus or Terence—authors of comedies who flourished during the Middle Republic—you will see liberal use of ego, tū and the like.  You should be aware that most of the Latin literature you will read is just that—literature.  As such it is carefully crafted and complex.  One technique of Cicero's, for example, is to construct sentences in such a way that vital information is withheld to the very end, at which point everything falls into place.  Often that vital information is who is doing, so the use of a pronoun woud give that away too soon.

You know that English is not really an inflected language, but it still retains a lot of inflection in the pronoun system (I say retains because English once was highly inflected, just like Latin).

              3^rd Person                                1^st person        2nd

Nom.   he         she       it                      I           we        you

Gen.     his       hers      its                     my       our       your

Dat.      him       her       it                      me        us         you

Acc.     him       her       it                      me        us         you

Notice that I checked 'gender' for pronouns in the chart at the beginning of this article.  I have to make one qualification: the first and second person pronouns do not inflect for gender, only for case and number, but the other pronouns do.  I suppose this is because gender would have been obvious whenever saying ego or tū.  Now let's move on and talk about adjectives and adverbs together.

ADJECTIVES AND ADVERBS

I'm writing about the two together because adjectives and adverbs serve to modify or qualify other words.  The simplest distinction between them is that adjectives modify nouns and adverbs modify verbs.  This isn't strictly true, but I'm sticking with it for now.  I don't want your head to explode!

Another reason for talking about them together is that they alone inflect for degree.  What's degree? 

Well, I might have a fat cat.  But you have a fatter cat, and Courtney's cat is the fattest of the three.  I run fast, your run faster, but Sue runs fastest. In these sentences, fat, fatter, fattest and fast, faster, fastest each indicate a different degree.  The three degrees are called, respectively positive, comparative and superlative.  The comparative is so called because it is used in comparisons: Garfield is fatter than Snoopy, Achilles is faster than Hector.  The superlative is so called because it is super!  Nobody is better than the superlative.

Now adverbs inflect only for degree since they only modify verbs, and any clause will have only one main verb—therefore, there can never be any confusion about which word an adverb modifies!  But adjectives have to change their shape (inflect) in order to show which noun they are going with (modifying).  An adjective will agree in case, number and gender with the noun it modifies.  This does not mean the adjective will have the same ending.  Nope.  (Also, notice how adverbs can't agree in case, number and gender with a verb, since verbs don't have these properties.)

I've already mentioned that nouns fall into five different classes called declensions.  In the same way, adjectives fall into classes, too.  There are basically four.  The first class is “1^st & 2^nd Declension,” and these adjectives are typically the first to be learned.  They are so called because they use the endings of the 1^st and 2^nd noun declensions.  The dictionary entry for these will look like:

clarus, -a, -um clear, bright, famous

The first three parts tell you what set of endings to use when modifying a masculine, feminine or neuter noun, respectively.  However, there are also “3^rd Declension” adjectives.  These are further classified as “three-ending,” “two-ending,” or “one ending.”  You know which kind of third declension adjective you have by looking at the dictionary entry.  Three-ending adjectives work like the 1^st & 2^nd declension adjectives in that they have a different ending for each gender.  Two-ending adjectives do not distinguish between masculine and feminine.  One-ending adjectives are so called because the Nominative singular looks the same in all three genders, although neuter still looks the same in the Accusative and Nominative and you find the characteristic Nom. and Acc. pl. -a ending.  Now let's take a look at the dictionary forms for these adjectives: 

            Three-ending:

ācer, ācris, ācre, sharp, fierce

The first three parts of this entry are the singular Nominative forms for masculine, feminine, and neuter, respectively.  Thus, puer ācer, puella ācris, bellum acre.  Also, note that the stem of this word is ācr-, not *ācer-.  You will see stem changes in the feminine and neuter part of the dictionary but not in the masculine.  So “of the fierce boy” would be puerī ācris; “of the fierce girl” puellae ācris and “of the fierce war” bellī acris, and so on. 

            Two-ending:

fortis, forte, strong

This entry is telling you that the adjective does not distinguish between masculine and feminine.  Thus, puer fortis and puella fortis; puerum fortem and puellam fortem.  Got it?  But you use forte with neuter nouns: bellum forte; bellō fortī.

            One-ending:

prūdēns, prūdentis, prudent

This entry is telling you that the adjective does not distinguish between genders at all in most cases: puer prūdēns; puella prūdēns; bellum prūdēns (an oxymoron?)  The second part of the entry is the genitive singular, and it is given so that you can identify the stem of the adjective, which in this case is prūdent- (why did the e lose its macron?)  Important note: even though these are called “one-ending” adjectives, neuters differ in the Acc. sing. and Nom. and Acc. pl., so that we have bellum prūdēns next to puellam prūdentem and puerum prūdentem,  and bella prūdentia next to puellae prūdentēs.  Yay!  I think this is enough on adjectives for now.