I have been emailed several times, wanting to know how to attach doll hair. This is the way I do it.
I cut the yarn to the desired length. I insert my needle into the first place I want to start attaching hair.
I usually put 4 or 5 pieces together, depending on the thickness of the yarn.
I fold the clump of yarn in half to find the middle.
Keeping the yarn folded, insert your threaded needle through yarn clump, be sure to go under entire group, come back around and insert back into head where you started and knot it, but don't cut thread. Depending how tight you stitched it to the head, you may want to put a couple of stitches to secure. Just insert your needle back into the head and come up in the next place you want to attach a clump of hair.
you can see how I keep coming up at the next point where i want to attach, when you have the desired amount, just knot off and secure your thread. Trim the ends if needed.
Well, I hope this helps, it is sometimes hard to explain things, but hoping these pictures give you an idea of how I attach the hair.