If you want to have others do a collab you created, you can make a drawing with a spot for them to draw their OC. Then you download the drawing by pressing the red arrow in the gear BEFORE you post it, upload the file to ufile.io, post the drawing you made for the collab, and then link the file in the comments. If you want to do a collab with someone else, you download the file they made. Then you go into beta editor (it's easiest in there in my opinion, but the regular editor works as well) and press the green arrow in the gear. You select the collab file and then you can draw on that file the person made. Hope this helped ^^