To signify your character doing some sort of action, you can do one of three things.
1- First Person Roleplaying. You would use the words I and we a lot. Example; I dodged the kick to the chest, and countered it with a blow of my own.
2- In this form, you would use *s a lot, as well as italics to signify that you are thinking. Example; *dodges kick to chest, then counters with a punch* That was close...
3- Third person roleplaying. This is where you are more like a narrator. Example; Blix dodged the kick to the chest, and countered it with a punch to his jaw. This is the most detailed style of the three, but also the most time consuming.
You can pick any on these styles to rp in.
Try to keep the storyline going. By that, I mean don't just post a bunch of one-liners to make the other person do something interesting. I ask that you post at least 3 lines most of the time. Not required by any means, but makes the roleplaying much smoother.
BB code is how you make things colorful, larger, centered, bold, or italicized. One way to do this is to highlight the area you wish to change, and then click on the action at the top you wish to happen. The other way is to type it. But there are some things you can't just highlight and click, which I shall explain.
Images- If you are trying to put an image in a post, you first copy the url of the image. Then, you would type [img], and then [/img. After that, you would past the image url in between the two. Make sure to put the closer at the end of it.
Spoilers- This would be used to keep a signature small, but still put in needed things such as other forms, or accessories. To do this, you would first put [spoiler], and then later on put it again, except with a slash.
Then, people would just click on it to see it, then click again to make it go away.
Everything else should be pretty simple and self-explanatory.