The circle at the right is actually a Trackball (think Blackberry) which helps control the cursor with awesome tactile feedback.
Keymat is a flexible plate of plastic, rubber or silicone which is put on the PCB of the keyboard. The rigid key tops are fixed on the keymat, so that they match with the switching dome below the keymat. Keymat is the standard techinique to make the logistics and manuacturing of optional keyboard variants feasible. The domes and backlight LEDs are soldered to the PCB of the keyboard, and the keymat is a "loose" component, which contains no eletronics. To disperse the light from the LEDs, between the keymat and PCB there can be a transparent plastic plate with holes for the moving key cap and the domes.