The both carry the same meaning: "Excuse Me". But there has to be a difference in their usage.
Please answer in English.
There are no difference, you can just choose the one that sounds better. "Scusami" literally means "excuse me" and "scusa" means "excuse", but "me" is implied anyway (at least when "scusa" is used as an imperative verb; it can also be a noun, and that is a wholly different thing). Both can be used both as "sorry" and "excuse me". Both are informal.