Go to http://www.ascap.com and/or http://www.bmi.com and you'll find all sorts of information.

Both ASCAP and BMI are licensing organizations, who work with publishers and collect certain royalties. Either one will tell you what you need to do; as to which is better, both have proponents, which is why there are two! (Actually, there are three, but I won't bother you with SESAC).