It's in the concepts manual! I've already pointed you at this specific link.http://docs.oracle.com/cd/E11882_01/ser ... htm#i16565
Yes, you can used both shared and dedicated server together. This section links through to the administrators guide, that explains how the configuration is done.
It's fine for you to search for explanations, but you should really start with the concepts manual, which will invariable link through to the other necessary manuals. Only after you've read all that should you look for other sources of information, that may or may not be correct. The Oracle documentation should *always* be your primary source of information.
The answer to all your questions are in there.