eh... it seems that you r a new one here to know about hair extensions or wigs, believe me, this is just your beginning. besides hair extensions, you will want to know wigs, synthetic wigs, human hair wigs, lace front, full lace, hair bangs, glueless full lace wigs, monofilament wigs... and so on.
well, hair extensions whether made of synthetic fibers or human hair, can make your hair thick, more volume or long. they have several kinds, clip in hair extension, fusion hair extension, or sewed in hair extension. you can bought it online or your local wigs store. i often bought it from Uniwigs, an online wigs store.