Describe how the multiplayer game will work in a few sentences and then go into details below.
Describe how many players can play at once or whatever.
Is your game client-server or peer-to-peer or whatever.
Describe how the players can customize the multiplayer experience.
Describe how your game will work over the internet.
Describe what gaming sites you want to support and what technology you intend to use to achieve this. Perhaps Dplay or TCP/IP or whatever. It is probably a good idea to break the tech stuff out into a separate area, you decide.
Describe if your world is persistent or not.
Explain how you can save a multiplayer game and then reload it. If you can or why this is not possible.