Who can play? Anyone! Just join the community, and post away. There's no application, no fuss, no muss. Join and play.
What can I post? Either a third person scene taking place somewhere in World's End, or a first person question/text etc for folks to respond to. Anything like that. You could also post a post that takes place in some other land that isn't World's End - just be sure to mark it as such.
What can't I post? Naked pictures of your grandma, ads for other games, memes and the like. Keep those to your journal. Likewise, extremely graphic or sexual content should probably stay there as well, if only to keep Livejournal happy. Links are fine - just let people know what they're in for before clicking!
What's in World's End? Basically, anything you want there to be! It's a town that exists outside the boundaries of space and time, so within reason most things can plausibly be there. There's a wiki to get you started - The Loft is a popular starting point. Interdimensional cafe, where can you go wrong with that?
Is there a live chat? Yes, there is! You are welcome to join and play live, or just lurk with us in the OOC room. You can find us on IRC at server irc.darkmyst.org . Join #The_Loft for OOC and #Charloft for IC.
Must I be a member of the charloft prompt community to play here? No, but we'd love to have you over there! So why not join both?
How do I tag posts? [location] whereyouare, [character] yourcharactersname will do.
What are the rules for playing? 1. In short, don't be a jerk to others, and try to at least be civil - World's End is a neutral territory where people are expected to at least not break out into open violence in the streets. Nobody likes meeting Mr. Stabs-Everyone-In-The-Eyes-With-Scissors.
2. Feel your need for character development isn't being met? Drop in to charloft and try some prompts; they might give you a good idea for your characters!
3. As mentioned earlier, keep anything extremely graphic / sexual to your own journal, and warn others when linking to such - it keeps the LJ server gods happy.
4. That's pretty much it! Just play the best you can and have fun with it.