Okay so I made a zipper pouch the other day, and a follower made a comment that she didn't know how to change a zipper foot WELL... while I am not an expert here are some picture that I hope help.
Step#1: Take your regular sewing foot off, on most if not all machines (to my knowledge) have a little button like this black one that my finger is on that you simply press and your foot will "drop" off.
Step#2: Take your zipper foot, it is divided down the middle, I always use the right side, but you don't have to.
Step#3: Line the zipper foot up and mine all you do is lower the arm and the foot will pop on, however, you may need to press the little black button again to get the "claw" to open up.
I am sorry this probably makes no sense, but if you have any questions let me know. I love putting zippers in, they really are fun and easy once you just bite the bullet and give it a shot.
PS. Sorry for the mess in my pictures, I am working on more zipper pouches YEAH!!!