It's easy^^ you need write this: [center] and then the group name : group name and the icon word, one more : (without space buttons) after "center" again [ ] between this ones, just before the center, you need write a / between the parentheses (but only just in the second one behind the group icon name) and will works :3

But well, FA use BBCode, so you can find so many option, choice here http://en.wikipedia.org/wiki/BBCode , or just search for the BBcode in Google^^