its

belonging to it

• That dog just walked on its back legs.
• That store is having its back-to-school sale.
• My car has a mind of its own.

it's

it is

• Guess what? It’s my birthday!
• Do you know if it’s four o’clock yet?

it has

• It’s been driving me crazy.
• I think it’s taken the waiter twenty minutes to come back.

there

1. Most of the time, there means “at that place” (the opposite of "here").
   • I went there to meet my brother.
   • I found my wallet over there.
2. When placed at the beginning of a sentence, there often has little meaning other than "something exists."
   • There are ghosts in that haunted house.
   • There is an old house on the corner.

their 

belongs to them

• All of those kids with their contagious laughter really made my day.
• They didn’t want to see all of their hard work go to waste.

they’re

"they are" or "they were".

• They’re going to a party tomorrow.
• You should meet my work friends; they’re a real hoot.

your

belonging to you

• I like your shirt.
• Your cat is hiding under the couch.
• I think that pencil is yours.

you're

you + are

• You’re sitting on my coat.
• I think you’re ready for the next level.
• He told me you’re a piano player

to

shows direction or aim

• I went to the store.
• She is going to school.

before an infinitive verb

• I tried to run really fast.
• We need to bake a cake.

too

excessively

• It’s too hot to go outside.
• This pizza is too salty!

also

• We live in Texas, too.
• You can come, too.

two

the number 2

• I have two sisters.
• Two of those dogs just ran away.

then

that time

• We were very tired by then.
• Since then, I have been afraid of clowns.

links items in a sequence

• She parked the car, then she locked it.

If . . . then constructions

• If you want more salad, then get some.

than

used to compare

• That dog is smaller than all the rest.
• Your paper is more wrinkly than mine.
• This book is harder to understand than the last one.

This is the spelling you’d use for more than, less than, rather than, or other than.