The forums have a BBCode
list in their help section.
I don't know which ONs & OFFs you're looking at, but I'll take a guess as to how they're formatted. Some of it may come from text wrapping around images, using the two float tags:
Also, a lot of the formatting is done by using the tables, which you can see in the link I provided. I also use them in various stickies in the public boards, as well as (most recently) in this thread
I'm actually currently working on creating a forum guide and FAQ, with one of the sections specifically for BBCode and formatting. If you have any questions, you're welcome to contact me or post your inquiries here.