you enter the work bench then hit the load button then you go to the top and hit saved or workshop the workshop one is where you download stuff off the workshop you hit the one you downloaded then you hit spawn the saved button is where your own things are at you hit the one you want then you can edit it and spawn it i hope this helped

if you meant how to mod your stuff you have to go to the workshop and download the mods you want then you go to the main menu and hit new game there you can hit the enable mods but you have to make a new world for them to work and when you have some or a lot of mods it will take some time to load in even if you have loaded the world a lot of times it will still take a good min