Staple your headboard wherever you want the buttons to go. This is the "tufting". Stapling the fabric and batting to the door will provide a little dent in which to glue your button.
I bought a button-covering kit from Joann's and used some leftover scraps from the headboard to cover the buttons. It would be cute to do a contrasting fabric, too. It's really easy, the directions are on the package.
Now, glue on the buttons! So simple, and it makes it look much more professional. The thicker the batting you use for this project, the deeper your indents will be. Try it!