Many digital cameras have really awful user interfaces. Mine is reasonably consistent. There's a wheel under your index finger, next to the shutter button. (Is it called a thumbwheel if you don't work it with your thumb?) Any time you need to adjust a setting or cycle through options, you use the thumbwheel. So to adjust the focus spot, you press the button for that function (yes, it's got a dedicated button), then use the thumbwheel to move the flashing LED to the point in the viewfinder where you want it to focus.

This is not nearly as cool as my uncle's professional model, which tracks your pupil and focuses on the part of the viewfinder where you're looking.