A baryon is a composite subatomic particle made up of three quarks (as distinct from mesons, which comprise one quark and one antiquark). Baryons and mesons belong to the hadron family, which are the quark-based particles
Nobody knows what produced the baryon asymmetry. There have been lots of suggestions but none of them have been demonstrated to be true.
What background reading have you done on the subject? I would have a look at the Wikipedia article on baryon asymmetry, and maybe Google for any related articles. If there is anything in these articles you need help with, post a more specific question here and we'll help if we can.