"Garry's Mod" ("GMod") is an online, sandbox-style computer game that allows players unlimited freedom in creating gadgets and scenarios. Admins of a "GMod" server are responsible for enforcing the rules of a server, can kick other players off and have more creation options than a normal player. If you are running your own hosted server for "GMod," you can make other players admins by editing the User.txt file your in "GMod" installation directory.
Open your "GMod" installation directory and go into the settings folder.
Find and open the file "Users.txt" with a text editing program, such as Word Pad.
Find the groups labelled "Superadmin" and "Admin". Delete the line that says "//garry" for both groups and replace with the name of the player you want to make an admin or superadmin.
Insert that player's Steam ID on the same line as his name, replacing the field that says "STEAM_0:1:7099" to say "STEAM_0:1:NUM", where NUM is that player's Steam ID.
Save and close the file. Reload the server and that player will be an admin on your server.
Players can find out their Steam ID by typing "Status" in the console.