Used to set up the server. The variables in here are all required to be set, and can't be changed once the server is created.
Is a dedicated server
The game description. Setting this to the full name of your game is recommended.
This should be the same directory game where gets installed into. Just the folder name, not the whole path. I.e. "Rust", "Garrysmod".
The version string is usually in the form x.x.x.x, and is used by the master server to detect when the server is out of date. If you go into the dedicated server tab on steamworks you'll be able to server the latest version. If this version number is less than that latest version then your server won't show.
If you pass MASTERSERVERUPDATERPORT_USEGAMESOCKETSHARE into usQueryPort, then it causes the game server API to use "GameSocketShare" mode, which means that the game is responsible for sending and receiving UDP packets for the master server updater. More info about this here: https://partner.steamgames.com/doc/api/ISteamGameServer#HandleIncomingPacket