^No joke. If you don't know Batman's origin story by now, you've been living under a rock.
The origin is mainly for kids and those completely unaware of Batman except just what's in merchandise or games or rides or something. The best thing to do at this point is jump in like everyone said and assume Batman exists in Gotham. If you have a young kid, you can explain the origin to them, if you are an adult and you don't know, google it. When BB came out, I rolled my eyes at another origin because I was a fan and accepted the origin from Burton's Batman, but now I enjoy Nolan's expansion of the origin, but now, Batman is beyond just the fans and readers of comics that unless it's going to be 10-15 years before another movie, there really is no need for it.