That is so easy to do, I sow my clips on myself. Basically, you need a needle, thread (try and get one to match the colour of the hair), and the clips and the hair.
1. Thread the needle.
2. Hold the clip in place, and make sure it is facing the right way, like the bit that you insert into your hair is facing outwards.
3. Put the needle through the hole at the bottom of the clip and then through the top of the hair like the weft bit and then through the other hold. You carry on doing this until you think it is tight enough. Then knot the thread and cut it of and do the rest of the clips!!
I hope this helps!!!