how do yoo lock the hair when you do invisible braids?

Answer 1

If you are talking about micro-braids, the tip of the hair (the tip of the braid) is burnt. Burning the hair creates a seal.

Invisible braids is also a term used to describe french braids. Here is an instructional on how to do a french braid:
http://www.hairfinder.com/hairstyling/french_braid.htm

Answer 2

allbraiding.com
hairogenics.com