Garry's Mod is a physics sandbox. It's an indie simulation game produced by Facepunch Studios and published by Valve in 2006. There aren't any predefined aims or goals. We give you the tools and leave you to play.
The system requirements are light; nearly any new computer will work for playing Garry's Mod.
Most gaming PCs cover the RAM requirement of 8gb, but 4gb is enough to meet the minimum requirements.