“This is How We Do” is a recently released song by Katy Perry. The chorus “this is how we do”, which is also a commonly used phrase, essentially it literally means “this is how we live” or “this is how we do it“. In this song Katy sings about the interesting things she does and how she lives, and is essentially letting people know “this is how we do things”. It's not much used as slang but a daily expression.