Vosric has a pretty good guide. http://www.thestarwarsrp.com/forum/index.php?threads/formatting-tips-and-tricks.72892/ You may have already looked at it though.
Zay also has a guide with some more basic BBCode stuff! clicky. If you have any questions, feel free to ask :)
@Dark child @Vosrik Those are very helpful, although there is a slight problem, the editing page doesen't open when I click 'More Options'
I suggest you use a Word Document, or Google Docs. Edit that, then copy and paste it into the SWRP text box. No need to go into More Options.
Hmm, are you trying to edit a post or write a new one? When you click 'More Options', it should open a new page where you can write in the Rich Text Editor (or the BBCode editor if you click the pencil)
There have been some issues with that lately. Abe is already looking into it: http://www.thestarwarsrp.com/forum/index.php?threads/no-more-options.73257/
You may have already looked at it though.