Usually there is a little hook type thing. That parts hooks onto the screw that holds your needle and then there should be a "regular" type of attchment same as all your other feet. I don't have a Janome but that's how they attached to my Bernina and Pfaff. Make sure you tighten your needle screw and check it now and then. I'm had it unscrew my needle and the needle fall out while sewing. When it hooks on your needle screw and the needle goes up and down, it moves the foot too, thus feeding the top fabric too.
I'd take a picture and show you but am at work at the moment.