My Bernina walking foot came with the guide and it fits into a hole right behind the foot part. Actually alot of your feet will accept the guide..you know that screw on the back that always is falling off?? Well, that is to tighten down when you put the guide into a hole on the back of the foot.
If you don't have a guide...you can always mark with 2" wide masking tape...just don't leave it on the quilt. Put it on...sew, then move it. You don't want the sticky residue on the quilt.
I bought several double needles. You use 2 spools of thread on the top..thread them both the same way and put one thread through the threads guides on both sides of the needle thingie. 1 bobbin thread. They make beautiful deisigns..I love using them!
Good luck with your binding...just jump in!