The end-delivery shuttle has a pirn which remains stationary, instead of a free-spinning bobbin. The weft yarn unwinds off the pirn's tip when the shuttle is in motion and stops unwinding when the shuttle stops. It comes off the pirn and goes through a set of tension pads and comes out of the shuttle at a constant tension, which you can adjust using the enclosed Allen wrench. This even delivery of weft causes less draw-in, which in turn makes better selvedges.
Resist the temptation to handle the weft yarn at all. Simply adjust the tension to suit the cloth you are making and allow your shuttle to do the work, making your weaving go more rapidly than ever.