Easy enough. Start OP2. Click Multiplayer. Click TCP/IP. Click either Join or Create (Only one player creates). Enter information.
Creating: Enter information. Make sure you select game type, and set how big the game is going to be. You should be able to figure it out from here.
Joining: Select either Broadcast to local network or Looking at IP address (In this case, enter information. IP is the one listed in the Hamachi window, beside player's name)