Apostrophes go in front of or after the "s" when making something possessive.
Example- Katie's book.
When you're making a contraction, it depends on what the word it to determine where to place it.
Examples-
It's a fun day.
We won't get hurt.
I wouldn't do that.
Please don't go.
I can't go to the park today.
Hopefully this is what you were asking!