download steamcmd
https://developer.valvesoftware.com/wiki/SteamCMD
1 . run installudpate
linux
bash InstallUpdate.sh
windows
click bat StartServer.bat
2 . run StartServer
linux
bash StartServer.sh
windows
click bat StartServer.bat
NOTE Change World Name And Password
save world
linux : $HOME/.config/unity3d/IronGate/Valheim/worlds
windows : %userprofile%/AppData/LocalLow/IronGate/Valheim/Worlds