Energy is good because it increases your damage and armor, and also gives a little bit of gold bonus - the more you have. It's always filled in the beginning of a battle.
Limit Breaks are powerful attacks, and the bar for it gets bigger when doing pretty much anything, but mostly for getting hit.
To use Diamond Bolt, click on your enemy, and press X to cancel the spell.
In the inventory if you hold over the 'help' button you can read some more.
Right-click game to play full-screen (if available)
To walk you can also press A,S,D,W. Press space to open inventory, where you can change sword. To use the map press CTRL, and SHIFT to return. While in the map, press Z to zoom, X to zoom out.
In battle you can, again use A,S,D,W and also the arrows. If you press space your energy will slowly sink, but if you press it while attacking you get a critical hit.
