Missing Buttons/Menus/Options

Okay, so in the upper left hand side of the...uh, Photoshop layout-a-rooney, there used to be a little...ya know, box or whatever that allowed me to change the size etc of a brush and also allowed me to toggle back and forth between [+] or "add" and [-] or "erase." It dissapeared months ago. How do I find it and put it back? Thanks.