Garryho Mod -

The core of GMod is building. You can start by spawning basic props and "welding" them together using the to create cars, rockets, or even complex robots.

While the single-player sandbox is great for learning, the game truly shines in multiplayer and with community mods: Guide :: Gmod: How to have fun - Steam Community Garryho mod

: Use the Undo (Z) key to quickly remove the last item you spawned. The core of GMod is building

Getting comfortable with the basic keybindings is the first step to mastering the sandbox: Garryho mod