well,

you create something on FA someone else can do with you and then you save the project and upload it on ufile.io and then you copy the link. Then you post your collab file and then you paste the collab link underneath the project. Then you wait for other people to do the collab. If you want to join someone else's collab then go to their collab link and download the file and then edit yourself only or stuff on the art collab and then when you're done name your post "Collab with (whoever you are collabing with)" and then post it!