Crazylegs Percy's discription is pretty good, I always chase the female thread first and as he said cut a (very small) spigot to fit snuggly inside the female thread, then on the male thread increase the diameter further up the spigot by 2depths of the thread plus a bit. Cut the thread and it will be a little tight, reduce the diameter a smidgeon leaving the thread visible and chase again, to strengthen the threads I take the tops off a little and also you can coat them with super glue or friction polish or similar. Once done rub a bit of candle wax on the threads. You may also explore tapered threads but that is a bit different. I would also recommend using an arm rest for the female chasing as it saves moving the tool rest all the time.
One last bit of advice, get hold of some plastic pipe and practice on that.