Adding the second player

Hello everyone im sure this question has been asked befor but was having horrible luck finding it. But here it is I am making a Fighting a=game and am wondering how to go about implementing the second player in,(no Ai at the moment). Not just that i am wondering how to go about making the character select screen for it as well, if some one know how to do it or has a video reference that could help it would be grate full, especially if it could implement both.