Although im having a hard time understanding what you mean, I will try to help you.

I think you try to ask: how to download besiege creations from the workshop, if thats the case, try this;

Go to the item you want to play with
Press subscribe
Check if it has the tag "level" or "machine"

If it has the tag machine, launch the game
go to any map
press load
in the right top there's a workshop button
then load the machine

If it has the tag level
Go to multiverse
host a server
Press load in the level editor
search for the workshop button in the left top corner
load the level

I hope I helped you out with this.