This is the wrong forum for this. Try hitting up the MM or AAM forums.
To answer though:
MSS = Message Storage Server
MAS = Message Application Server
The MSS acts as a central storage location and administration front for subscriber mailboxes. The MAS servers are simply the front end for the system, typically connected via PRI, H323 or SIP.
I'm not sure on MM how to view the connected MAS, it's likely through the Web UI on the MSS. on AAM, you can view it in the topology section of the MSS.
This architecture applies to both AAM and MM.