It is very simple:
The first option, lets you go online and wait for a connection (you will have to enable this, and be connected to the Internet for others to connect to your computer).
The second option is to connect to a computer that is 'online' (you will need the IP address of the remote system), which will display a message on the 'online' system's screen, requesting the user, if Maniac should allow the user from a given IP-address to connect - and once the remote user clicks 'yes', the game starts and the Chat window is opened.
Please note that the 'server-side' computer (the one that waits for the connection), does not get to decide the type of variant, the starting position, or the side to play. All this is decided by the 'client-computer', where the user may choose the variant, accept the default starting position or setup a new one, and choose the side to play - then when he/she connects to the remote computer, the remote-computer will accept the opposing side, and setup the position accordingly.
Please note that, even though Maniac allows you to 'chat' during play, you may not do it, once the connection is disconnected - so you will need some other 'online' program (such as ICQ), to pre-arrange the game to be played, and decided who will act as the 'server-side', and who will be the 'client-side'.
The 'disconnect' option will disconnect any current connections - and you may also use it, if you have a problems connecting - that is to disconnect any current connections, when the opposing player has disconnected.
The 'Send Wake-Up Message', is an option, incase the opposing player has close his/her chat-window, and you wish send a message to that person.
If you are running a firewall tool such as ZoneAlarm, then you must allow Maniac to act as a server and as a client through the port 3214.