The specifics:
Face and minimap are self explanatory, I hope.
The red bar is hp.
When the hp gets into the cyan area, your limit starts charging, which fills the cyan bar. You can only use your limit when it's charged.
If the hp falls below the edge of the purple bar, you lose control of your pet. The purple bar represents its health.
When hp falls below the edge of the yellow bar, you can no longer use items, though health potions are still usable. Using items charges the yellow bar, which increases the effectiveness of your item.
When hp falls below the edge of the green bar, you can no longer use skills. Holding down the skill button charges the green bar. Using a skill when the green bar is fully charged uses the skill's more powerful version.
Attacking with your weapon charges the navy bar. Attacking when the navy bar is full uses your weapon's skill.
Now think of the combos I can make with this.