First of all, you need to understand that when there is an apostrophe in a word in English, it means that it is a smaller version of a group of words. When the apostrophe is used, the meaning of the sentence does not change.

Examples : 

You’re → You are

He’s / She’s / It’s → He is / She is / It is

Does not / Do not→ Doesn’t / Don’t

There is / There’s