Because the changes to the 10.1 library model were so substantial there has been a huge amount of info on updating and they way this model affects organization put out by Apple and many training organizations.
Here is a very good document by Apple; it gets right into the files created by updating. There are other docs by Apple as well as articles and free video tutorials by trainers easily found by a search.
The short answer is events live in libraries and projects live in events. Left to its own devices, the first time 10.1 is launched it will update the projects and events it sees on connected drives and make a library for each drive. The disclosure triangles reveal collections. If there are no collections, nothing will show when opened.