Transfer details from international flight to domestic flight and vise versa.

I will be going to Beijing by Qatar Airways, and then to Dalian by China Southern Airlines. While coming back I will be taking the China Southern Airlines from Dalian to BJ, and then Qatar Airways to Oman. After reading the information on the PEK Airport Guide, I understand that Qatar Airways arrives at and departs from Terminal 3, and China Southern Airlines arrives at and departs from Terminal 2. How far are the two terminal buildings from each other. In order to transit, how do I get from T3 to T2, and vice versa? I have about 3 hours transit time each time. Please explain in detail. Thank you.