razor haircut?

i just got my haircut a couple days ago, I trying to grow it into a shag but it's way too short, anyways the back of my hair doesn't hold on very well and before it was like 4-5 inches past my ears, now it's like 2-3 inches, so it's kind of fragile, i heard a razor makes your hair like glued on your head if you know what i mean, for those short haircuts, but i haven't used a razor before, will it make my back really tapered? And how different is it from scissors or clippers?