How to Host a Server on "GMod" With Hamachiby Seth Amery ; Updated September 22, 2017
"Garry's Mod" is a physics game without predefined goals or aims, and you can play it by yourself offline or with friends online. While most players need a dedicated server to have friends and strangers join a game, you can create a makeshift server using Hamachi. This functions as a type of local area network, or LAN, and it does not have a monthly cost like dedicated servers do.
Download Hamachi to your desktop. Double-click the downloaded file to install it. Upon completion, the program automatically opens.
Click "Power On," and wait several minutes for first-time setup to complete.
Click "Network," followed by "Create a new network." A dialog box appears, asking you to select a network name and password. Fill in these fields, and press "OK."
Load "Garry's Mod" to the main menu, and select "Multiplayer." Check the "LAN" box as you set your desired options onscreen.
Press the grave/tilde key (` / ~) and type "sv_lan 0" without the quotes. Press "Enter."
Have your friend open Hamachi and join your network. Have him click "Network," followed by "Join an existing network" on the program. Using your network name and password, he joins your network.
Have your friend open "Garry's Mod," and select "Join" under "Multiplayer." Give him your LAN IP address, found on the Hamachi program under the power button. Have him type this in the "Server Address" box, and he can join your game.