since multiplayer is a different executable, it has different cheats. to cheat in MP you have to first start a server with cheats enabled, by doing "devmap mapname
" and then typing in whatever cheats you want to use.
god - makes you not die
give - gives you whatever you put in, there is a lot of stuff, give all gives you a good bunch of things.
noclip - lets you fly around without touching walls
timescale x - replace x with any real number, 1 is default, this slows or speeds up how fast 'time' goes on the server. for example, timescale .5 means everything happens at half speed.
npc spawn name
- spawns said npc's, there is a large list of them
try looking here