"what's this energy thing"? 
Energy in Demigod is like Mana, or using a Sins analogy - antimatter  It's used for all abilities.
 It's used for all abilities.
"where is my life meter?" 
The green bar to the left of your Demigod's portrait. The blue bar to the right is your energy.
A few other notable buttons:
- Bottom left of the Demigod portrait is the skill tree button. Clicky to see the skill tree and there will be a count of available points in the top left (1 point per level-up).
- Bottom right of the Demigod portrait is the stats button. Clicky to see all the numbers - damage, attack speed, armor, speed, hp/energy, equipped items, etc.