This one’s for Auntie.
Two is, of course, a quantity.
I’ll have two desserts, if you please.
To is most commonly used as a preposition to indicate direction.
Please bring your book to class with you.
I’m going to the store before it closes.
Too is generally an adverb that describes degree or indicates inclusion.
She is too good for that guy.
I thought you were coming, too.
Your / you’re
Your is a pronoun that is used to indicate possession.
Your sister called to say she’ll be a little late.
Don’t leave your socks on the bathroom floor.
You’re is a contraction that means you are.
If you don’t hurry up, you’re going to be late for your interview.
If you don’t want to sit in traffic, you’re going to have to take the back road home.
Then / than
Then is most commonly used as an adverb that indicates time or sequence:
Put on your snowpants first, then put on your boots.
If you don’t try, then you’ll never know if you can do it.
Than is a conjunction that is most commonly used for comparison or contrast.
She makes more money than I do, but I’m a much nicer person.
These words all serve different functions in the language – there’s a lot more to them than what I’ve given here – but these are the most common uses.