Those things at the top? Most of the times they have a R and a L on it. Facing the front of the drive put the L on on your left and the R one on your right. DVD drives generally have several screw holes where you can put the, just play around with it.
When you slide it in they should click and lock. It's normal to be sticking out if the front of the case is removed, once you add the front panel back it should line up nicely.