It's very easy, once you find instructions that don't go into so much detail that they end up confusing you. Sometimes A, B, C, D works much better than A, B, C, D, E, F, G, H.
A: Make a slip knot at the end of your yarn and slip the loop onto the left prong of your hairpin lace loom, having the knot at the center of the loom and the working end of your yarn draped over the right prong. Put your bottom spacer on to hold this in.
B: Bring yarn around the back of the loom, insert your crochet hook from the bottom through the middle of the left loop, catch the working yarn and pull it through.
C: Keeping loop on hook and holding the working yarn in your left hand, flip the loom over, going from right to left and passing the hook through the middle of the loom. (Don't drop the loop from the hook.)
D: Insert hook through the left loop as before and pull the yarn through. (you'll have two loops on your hook now) YO and complete the sc to get back to one loop on the hook.
Now, repeat C and D until you have the specified number of loops on your strip. making sure that you have an equal number of loops on each side. Then cut your yarn, leaving a decent tail, pull it through the last loop on your hook and tighten to end your strip. If you need more room on your loom, simply remove the bottom spacer, drop off all but a few loops, then put the spacer back on and continue making loops. Once you start dropping loops off the loom, be careful that you don't twist the working yarn around the strip. This is easy to do and easy to prevent, just keep them separated when you're flipping the loom. However, you can get a pretty large number of loops on the loom before you have to do this, just scrunch them together as you near the top of the loom and you should be able to get at least a couple of hundred loops on there before you have to make room for more.
If you do this right, your yarn will always be in the back of the loom and will always wrap around the right prong of the loom each time you flip it. You'll soon find a rhythm and a way to hold it all that will suit you, I'm not going to tell you how I hold mine because it may not be right for you. Once I found some instructions that made sense I was off making my first strip and it really works up fast. I'm going to make a wrap out of it from some leftover stuff in my stash and see what joining method I like for it.
The instructions that finally made sense to me are here if anyone is interested. They may not make sense to someone else, but when I read them and tried it, everything suddenly clicked and I was making hairpin lace instead of a mess.
One last piece of advice if anyone is reading this: Don't hold your yarn too tightly, just tight enough to make the loop around the fork. Pull it too tight and you'll pull in the sides of the loom and have an uneven strip.