top right
bolt count, used for buying weapons and ammo.

top left
ammo count of current weapon plus its level progression (red bar)

top center
This is your current health. Your health gage is made up of little lines forming diamonds. When they are filled in you have health there, when they are hollow they do not hold health. You fill up your lines with the blue spheres you find on the levels. The red progress bar is progress towards your next health increment, and it builds up when you kill any enemy.

Ratchet and Clank 2 Going Commando Walkthrough