grammar - whats the difference between し and と?

I thought I knew this but it has just been explained to me in Japanese class and now I am totally confused.

I had always thought と was "and" but apparently it more usually means "or"; when you want to use "and" you should use し at the ends of words? Is this right?

Or is し only for reasons? Surely there are cases where its borderline if you're giving reasons?