[quote=@vankali]1. So, someone makes a plot then others would join up and create their characters. What happens next?[/quote]

You have your setting, you have your characters, the ball can roll. If it's your RP you devise and app for them to fill out to compile their character information on or if it's someone else's you fill out their application with your character information and get accepted, maybe.

[quote]2. Is it necessary to make a post everyday to the topic you joined?[/quote]

No. Though it may depend on the GM. Personally I don't stress forcing people to post so in some RPs we can go days or a good week between posts. But in my later mentioned RP most of our posts are chapter-length so I can't rush them.

[quote]3. How does the RP ends?[/quote]

It ends when it ends. I haven't ever gone that far, and my longest running RP (four years total, a month until one year here) has been written with no real common idea on what the final outcome will be. Most of us have an idea on where we want our major plot threads to go, but it's been written as a continuing story.

[quote]4. If I were to make the plot, e.g. I created a setting that was awesome to be put into an actual game(I'm not saying I'm so good, just asking if ever that happens) then somehow my idea/concept was copied/used by someone, will I get any credits?
[/quote]

Unlikely, but I wouldn't get my panties in a bunch over it. This is forum RP so it's not exactly the most high-class style writing. A way to tackle this is to think of it as "just practice" if you have any aspirations of going anywhere. "Theft" would be a common thing to see, but we're all doing that anyways: we're all borrowing the same tropes or even the entire concepts of established works - if not blatantly stealing the work itself for fan RP - and reapplying them for our own use.