From the top: First, any key will light up the backlight (so no option to leave it off). Top left is the Power On button, on the right is the Off button (press twice to turn off). Right below in the center is the lamp mode button. Surrounding it, and on the next row, are four buttons for different aspect ratios: 16:9, 4:3, Letterbox, and Native.
Further down are direct access buttons. In the center is the mode control (Bright, Cinema...), and to its left and right are Brightness and Contrast.
On the following row, you'll find Edge Mask on the left, Overscan on the right (you can choose one or the other, but both can't be used at the same time. Overscan gives you a slightly smaller image, chopping off the outermost pixels to remove unwanted image noise that is not unusual from cable and satellite source material (and some standard DVDs). Edge mask, instead, simply gets rid of the same "junk", making the overall image a slight bit smaller. I personally favor edge masking (though many projectors lack it). It allows you to maintain 1:1 pixel masking for the sharpest possible image, while overscan expands the image that's left, which is going to be less accurate, and a bit softer.
There's a source lock button between those two. Your choices are having the HD20, when powered up, going directly to the last source used (say HDMI 1), or searching for the first source it finds. Some like it one way, some, the other.
Next comes the navigation area, with arrow keys in a round formation, and the Enter button in the center. The menu button is just below to the left, in a comfortable place.
And that covers it, except for the five lower buttons, which are direct access buttons for the different sources (HDMI 1, HDMI 2, Component video...)