PBL is like a study group of 9-10 people that each have to study for one of the things that they don't know about a case. Each do the research and present it in the class for others. Basically you teach each other. There is a faculty in sessions who guids every thing and any thing you need to know. If you miss to know something they step in and ask questions or straight out give the information you need to know. Some schools like USC teach some courses solely with PbL. Some like Case have a hybrid of traditional lecture and its Pbl. It's alright in the hybrid form. But its stupid to try to learn everything this way in my opinion (as in USC). And it's not difficult to adapt to. Nothing to worry about.