Facebook Button in Amazing Grace theme

I am using the Amazing Grace theme and I would like to add a simple Facebook button next to the large RSS button that is in the header. I am new to php and other forms of code so I’m not sure where I should put the code for this and what code I need to use for the header.php file. all I want is a graphic button that is href’ed to a facebook address for a group. If anyone knows how to do this I would greatly appreciate it. thanks.
Tim