I want long, thick hair. Some of my friends by fake hair, make braids to their hair and then sew fake hair in that. Can I do that with this hair, like using it as a extension?

You can, but really what you are describing is more like a "weft" - which is a strip of stitching with hair that hangs off of that. This hair is loose hair and is best used for braiding or building into other hairpieces. :) You might look at wefts or "weaving" hair for something to sew onto a braid.