You just cut it out of the animal, trying to get as much length out as possible, then let it dry a day or so til it's rock hard. Then you bend it, twist, and pound it, the idea being to start to see it crack and split into fibers. (Bend it all you want and don't worry, you can't break sinew with your hands no matter how much you bend it) . When you have the fibers the thickness that you need, you either chew them like they said, or soack them in cold water, not warm and for darn sure NOT HOT! Warm or hot water damages sinew and can ruin it. Also, when you pound the sinew, be sure to do it on smooth surfaces, not cement or anything that will scratch it or tear it during the pounding process. A smooth river rock, or hammer, on one of your wife's meat boards is fine.
~~Papa Matt