When I download an adv_dupe build and extract the files to the adv_dupe Folder, how do I use the builds in-game?
You get out the adv duplicator tool, click the dupe in the Q menu, and click open.
Left click on world to paste.
Right click to copy. And after you copied something, bring up the Q menu again and you will see an option to save it. Next time you can load the contraption again by pressing load.