Server App - Control Array of Sockets.

I need to create a server application that can have multiple users connected to it, so I'm going to need a control array of sockets. I'm not to familiar with control arrays. I need my server to use "ack" responding for its system of how it works. Anyways if someone could tell me some things about control arrays that would be helpful. Thanks.

Oh, and if you dont know what "ack" responding is it's:

-Client Sends data to server
-Server sends acknowledgement and requested data