When can I use "pardon"?

Hi Ana, 

The use of 'pardon' and 'pardonnez-moi' is stronger in French than in English.

You might use it if you bump into somebody by mistake but you wouldn't use it for something trivial like not having the exact change in this situation.

You are actually asking someone to pardon you for doing something wrong.

The word I hear most for saying sorry is 'désolé' .

Bonne Continuation!