How do you extend braids with thread?

I have seen street booths at festivals where they braid a small section of hair by the scalp and attach colored threads and beads to it. Normally, it will hang down longer than your normal hair. What is this called and how do I connect the thread to the braid? How many strands do I use, is it washable, and so forth. I want to do this and add feathers instead of beads.

Thank you much!
Runningcow ;-) <><