As important as saving is in Garry’s Mod (if you don’t already know how to save, check here), what’s even more important is knowing how to load those files. Particularly, it’s good to know how to open up saves downloaded from the Workshop. Have no fear, person who is probably not scared at all, loading a file is a pretty painless process overall.
First up, you’re gonna want to get to the list of game saves. Hold down Q to open up the menu, and head to the Saves tab towards the right. Click on the save file you wish to load, and then click the handy “load” button. You can also limit the selections to your saves by clicking on “My Saves” to the left. Viola, now you’re free to continue whatever madness you were working on.