Cropping quesiton

Possibly a dumb question, but I'm at a loss at what to do.

I recently converted from a PSP user, to a PSCS3 user and I'm trying to figure out how to crop an image.
In PSP, you can select the hight & width, and it will automatically give you the crop box, but in PSCS3, it's not doing it for me. I'm trying to make crop some images for icons, and it makes me resize them myself, and the images always end up not being the size I want.

So, how do I crop? I'm completely lost at how I do it.

(I hope this post made sense).