Forum play can be useful for single players who want to write scenes that just involve their own character/s.   Multi-player play can also happen using replies.   Please give your thread a useful title that includes character and general info, eg: "Sophie finds a stray kitten".   At the start of your thread, please make it clear whether or not you are open to collaboration.   You can do this within the prose - eg: "Sophie is in the bar alone, and the doors are still locked." - or by using ((out of character double brackets)) to make a note at the start about how open you are to others joining the scene.   If nothing is noted, the assumption is that anyone can join your thread with their characters.