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)