Couple questions about thinning shears?

Okay so I trimmed my bangs a bit and now they are too blunt, even thought I tried to point cut them. I bought a pair of thinning shears but I don't know exactly how to use them. How far up to I put them in my bangs? And they wont make my bangs any shorter, right? Because I like the length perfect, I do not want them any shorter. Just thinner. Please help me before I completely mess them up lol =]