How Does Microgynon Protect One From A Pregnancy?

Hi, I've been taking microgynon for a while now but I don't understand how it protects me If I have only taken two pills for example after my 7 day break am I protected? If I have sex on the same night as my last pill in the pack, again am I protected? I don't understand if I covered from pregnancy all month if I take it correctly. Please help