Yup, there is a difference. Tug straps go through the skirt (not the sheepskin) and tack, nail or screw to the tree, they do not go through the front, seat or back jockys. Strings may or may not go through the tree and skirts but they do go through (or come out, depending on your view point) of the jockys.
Stohlman shows one set of tugs at the front of the tree and two sets in the back per side. That's what I do and it has worked well for me.
Best regards, Josh