Hello people!! We are about to embark on a fantastical journey of grammar and language. I find it interesting that people like to call themselves speakers of the English language, when they do not actually understand some of the most basic rules of it. Anyway, the first topic will be the ones discussed in the title.

Your vs. You're
Something that just makes me seethe on the inside is the infuriating simplicity of the rules of these two words. I'm serious. It's really not hard. And the worst part of it is that I see people of reasonable intelligence mistaking them all the time, including all the "good" writers on this website who often are extremely annoyed at the "n00bs," when they themselves don't have particularly good grammar. However, I have to admit the the "n00bs'" grammar is generally worse. Anyway, I digress. I believe I was talking about the infuriating simplicity of these two words. Look, I'll put it in simple terms:
Your: your is a possessive pronoun. This means that if I say, "This is your hat," your is referring to the hat belongs to you. Therefore, your should only be used as an adjective describing something the belongs to *you*.
You're: you're is a contraction of the words you are. This is why there is an apostrophe there. You know, this thing: ' . Tell me, would you consider saying doesnt? Or dont? No? Than why do you feel you're is so inferior to other contractions that it's so hard to remember that it needs an apostrophe to stand in for the letters it's missing!? For example: "You're going to die if you continue using bad grammar." See how that can also mean, "You are going to die if you continue using bad grammar." "Your going to die if you..." does not work because what belongs to you? Huh? Your is a possessive adjective, what do you possess in that sentence? Can't figure it out? That's because it's wrong!!

Next on my agenda is:

Who vs. Whom
Warning: If you don't know some of the basic prepositions, almost everything I tell you in this won't help you at all, as prepositions are vital to knowledge of who and whom. Now, these can get a little more complicated. In order to explain them, I will need to go a little deep into noun functions. If you don't want to bother with that, I'll write a little section at the end of this "segment" telling you how to avoid using whom so you don't look stupid. Anyway:
The first think you need to look at with these to is that nouns can be divided into two categories: subjective, and objective. Subjective nouns are nouns that are, surprise, part of the subject, or something of the such. Objective nouns are nouns that are the object of something, like Direct Object, Indirect Object, and Object of the Preposition. With whom you will always almost encounter it as an Object of the Preposition (for convenience's sake I'm going to refer to it as OP from know on. Remember, OP = Object of the Preposition) Some common prepositions you will see it as the object in are with, for, and to. Because whom is an objective pronoun (the objective form of who, which is subjective), you may only use it as an objective noun, since pronouns stand in the place of nouns. Examples of when to use whom with the prepositions I gave you above are:
To whom are you sending this gift? (Common mistake: who are you sending this gift to?)
For whom is this gift? (Common mistake: who is this gift for?)
With whom are you going to the party? (Common mistake: who are you going to the party with?)
Now, sentences in English are almost never allowed to end in prepositions, so this is how you know to use whom. Chances are, if you see "Who are you going to the mall with?" it needs to be whom. However, beware of phrases like look up, or lied to, or other phrases that end in prepositions, because you could see this, "Nobody likes to be lied to." This sentence ends in a preposition, but it is still perfectly fine because lied to is an acceptable phrase that happens to end in a prepositional phrase.
Who: is a subjective pronoun, which means it will either be the subject, subject complement, predicate adjective, or an appositive (I don't feel like explaining what all those mean, and it won't make much of a difference anyway). For example, "Who is this?" In this sentence, who is the subject. Therefore, it is a subjective pronoun.
Whom: whom is an object pronoun. The means it can only take the form of objective nouns, and it is almost always an OP. For example, "With whom are you going shopping?" With is a preposition, thereby making whom the Object of the Preposition, which means it's objective.