A lot of words in the English language (and possibly other languages) sound the same but have different spellings and/or different meanings. The problem is that a lot of people never learn these different spellings and meanings and just go about their merry way using the wrong words. When somebody is speaking, you can't tell. However, once you start writing stuff, like web pages or email, you make the big mistake of confusing your readers. People that don't already know what the right homonym is will learn it wrong, from your usage. Those that know the right word will just think you're a moron. So what should you do? Learn it right!
There is usually used to describe a physical place or location, or at least a noun. It can also be used in other ways, but I don't know how to best describe it. The following examples should help:
Their is used to show possession. Just as 'his' shows possession of an object by 'him', and 'her' shows possession of 'her', their shows possession of an object by a group, they.
They're is a contraction of the words "they" and "are", as indicated by its apostrophe. You use it to describe a group of objects or whatnot. If your sentence doesn't sound right by replacing they're with they are, then you're using the wrong form of there/their/they're.
To is hard to explain. It's kinda like an implied verb prefix. Read the examples.
Two is the spelling of the number 2. Use it when referring to 2 elements of something.
Too can mean either 1) also, or 2) an excess of.
Are is hard to explain also. Read the examples.
Our shows possession. Use it when you are referring to a group you are in that 'owns' something.
Your shows possession.
You're is a contraction for "You Are". If you can't replace you're with you are and have your sentence work, then you've messed up.
Its is the possesive form of it.
This is the contraction of the words "It is".
See if you can identify the correct sentence....