Where vs. were vs. we're

Look at the following sentences. The sentences contain the words where, we're or were. Try to find a pattern and see if you can discover when you should use where, we're or when you should use were.
 

I went to the store where I bought my favourite sweater,
Where did you go to school?
So that's where Ieft my keys.

 

We're going to be late if you don't hurry up.
We're not coming to the party.
You mean we're that close?

 

They were very mean to me.
Were they interested in the book?
Those girls were at the party too.