I don't know how to make a 'server message', how do you make one?

a few ways of doing it.
1) edit soldat.ini. you'll come across something like server message=If it bleeds we can kill it etc. change it to what you like.
2) If you have registered you can edit specific profiles under the profile directory etc. if you're called hi1000 try looking for hi1000.ini and follow the directions in 1
3) Run Config.exe from your soldat root directory and go to one of the menus there it has a server message form you can edit!

thank you!