Welcome to the Guild! If you don't mind me asking, what are "polyvore/urstyle" Roleplaying? I've never heard of those terms before and my curiosity is certainly peaked.
polyvore was the original site, but urstyle has replaced it since it died
in general, the format is as follows:
-GM (mod) writes up "pre made characters" (like a paragraph or a few bulletpoints about the character, sometimes with provided name/age/fc). people pick which pre-made they want to write for, and multiple people can "audition" for the same character by filling out the CS
-CSes (auditions) are accompanied by "sets", aka collage-ish things to show the aesthetic and stuff of the character
-GM picks who gets to play each character after CS/audition process is over
-usually followed by a plotting period, where people message each other with ideas and char first impressions and such
-the "IC RP" itself is basically one post ("story") per event (GM provides lil blurbs about each event), accompanied by a set for each event. people would make the set and ask people to comment to include their characters and/or work out inclusions via PM beforehand. there's a greater degree of freedom re: controlling other people's characters than there is on here (you can write into your story that someone else's character said something or w/e, and obviously if the person who the character belongs to objects you change it but more often than not people don't seem to have too much of a problem)
not sure how well I explained this but happy to link examples lol
there are definitely exceptions to the general format most people have done -- i'm THAT bitch and don't really like story RP style, so my rps on there tend to be more aligned with how things on RPG usually go lol