Spawn a drivable vehicle by going to the Spawn Menu > Vehicles.
How do you enter vehicles in Garry’s Mod? You’ll then see a prompt, where you can type “sv_cheats 1” and then “thirdperson.” If your server has cheats enabled, you can just type in “thirdperson.” Type all of these without quotation marks, by the way.
Open your Steam Library, right click on Garrys mod then click 'Properties.', on the following window click on the 'LOCAL FILES' tab and finally click the 'BROWSE.
Hit the tilde on your keyboard (it’s the little squiggle: ~) to bring up the console.