1. Put the ends of the pin perpendicular to your head and hook some hair with them.
2. Lower the pin so it's more flat against your head and wiggle it up and down as you slide it into your hair (almost like you're sewing). This will help you grab hair from both of the sections that you're pinning together.
3. Push the pin in all the way.
If you do this correctly, the pin should be completely hidden. The key to hiding it is making sure you put it in perpendicular to your hair, as mentioned in Step 1.