For a start, when you are reading about connections, you are really talking about normal user connections, rather than background processes, so I would think of them as completely separate things.
Each session/connection has it's own PGA. That's were it holds session-specific details, like package variables, cursors and depending on the processing, full table scans my be read directly in to the PGA and bypass the buffer cache entirely.
The session does not connect to the SGA via the PGA. They are completely different memory areas. The server process associated with the session does some operations using the PGA, but for others it uses the contents of the SGA. One is not a link to the other.
Regarding my online time:
This website is not. I log on whenever I have change and try to answer questions. The frequency depends entirely on what is going on in my life and where in the world I am. Next week I will be at OOW2013, so I will be in West Coast USA time and I will probably not be answering many questions as I will be at the conference. Like I said, it's not my job, so I do what I can, when I can.
No you can't upload anything. This forum should just be for simple questions. Uploading documents and stuff like that is not appropriate. If it can;t be put into a couple of paragraphs or a simple SQL test case, you probably shouldn't be asking it here and I probably don't have the time to answer it.