We give you the tools and leave you to play. You spawn objects and weld them together to create your own contraptions - whether that's a car, a rocket, a catapult or something that doesn't have a name yet - that's up to you. Garry's Mod is a physics sandbox. There aren't any predefined aims or goals. You can do it offline, or join the thousands of players who play online each day. You can place a variety of characters in silly positions. If you're not too great at construction - don't worry.
more information...