Getting the foot to stay on...?

Question

I am trying to keep the foot on...I'm not sure if there is something else that goes on this machine. I'm very new to this, have used this machine once in four years. It's been sitting in the closet, and I'm now learning to sew with my mother. But now that I have my machine out - I can't get the foot to stay on. My mom's machine has a clip....but this one has a s***w and I'm not sure how it attaches. Could someone help me out? (I've lost the instruction manual...)