When we look at pictures of feet for sale we take the picture and turn the feet around in our mind's eye and look at it from the side and imagine a ruler behind it. I think you are not strong in picturing an object in your mind's eye. That is Ok. We have cheap photos now and can take a lot of pictures instead. No need to imagine. Just take your nearest camera and the feet you have now that you KNOW they are low shank. Line up the camera shot the same as the pictures for sale have it and take a picture. Now you have a picture that you KNOW is low shank and is lined up the same as the pictures for sale. No need to turn anything in your mind's eye.
That will not help quite as much for the buttonholers and monogrammers. You will be able to take your low shank picture and compare it to the _shank_ of the buttonholer or monogrammer foot. And so you will not buy a high shank monogrammer or a top clamp buttonholer by accident. But I do not know enough about Kenmores to know whether there was more than one kind of low shank fancy attachment.
When the set for sale says "snap-on" and also "adapter" the adapter is for putting on a low shank machine. The feet snap on to the adapter, the adapter stays screwed onto your machine.
Here is the online manual link again. It has drawings of the optional accessories you want but only from one angle.