A DUPE file contains an entity used by Garry's Mod, a physics sandbox game that revolves around building random objects. It stores an entity, which is an object, such as a chair, vehicle, building, or person that can be deployed in the game. DUPE files are used to share entities created by users with other users.

You can create an entity in Garry's Mod and save it in a DUPE file using the in-game menu. You can then upload it to Steam Workshop to share it with other users. You can also download DUPE files available in Steam Workshop to use in your own game. After downloading the DUPE files, you should place the files in the following location in the game installation folder: \GarrysMod\garrysmod\dupes You will then be able to access the entities in the DUPE files by selecting the "Dupes" tab in the in-game menu and clicking "My Dupes."