Eelskins basically have 2 uses when it comes to striper fishing:
The Skin Plug - Take all of the hooks off of a swimming plug like a Jr Atom.
slip an appropriately sized eelskin over the plug. Adjust overhang at end of
plug to suit your desires (usually 3" - 6"). Secure at the head with
cotton string. Replace the belly treble(s) with new ones. Don't use a tail
hook.
Eelskin Rig - A special jig which usually has a second hook attached to the
jig via twisted wire. Slip eelskin over rig. Secure at head. Adjust trailing
length to suit prevalent bait fish or desire. Puncture skin with hook(s) so
the skin streams naturally.
In both cases the skin is usually inside out (blue side out). The dark side
of the eel skin goes up.
The skin plug is usually fished near the surface. The Eelskin Rig is bounced
along the bottom. The Eelskin Rig is used practically nowhere but the Cape
Cod Canal.
There is a similar rig (usually homemade) that can be used for trolling eelskins.