Add new button to the toolbar

Hello
I want to add a new button to the fck toolbar.
The problem is that I dont know how to do that.

I want to add button that at the press add to the text area simple string like "hello world"

In general I want to add code button like the BBCODE.
It will be better if I will mark string and the fck system will add string beafore and after to the marker string. like the BBCODE system in that forum

thanks !

I sorrry if I have some english mistakes. I don't speak english.