There are two ways to use spells in Allods Online. You may right-click on any spell in your Spellbook or action bar. Your character will then begin using this ability. Spells do not automatically repeat once they have completed, so you will need to right-click on the spell to use it again.
Additionally, you may also use the hotkeys that correspond with each spell on the action bars. Once again, spells do not automatically repeat once they are completed, so you will need to continue to press the hotkeys to use each spell.
Most spells have cooldowns, which means that after they are used they cannot be used again for a certain period of time. Spells whose cooldowns are active will have a grayish color covering their icon. Once this cooldown has faded, you will be able to use the spell again.
Certain spells can be prepared in advance which will remain queued until you cast them. When you are ready, you can cast them by clicking the spell on your action bar or pressing the corresponding hotkey. Once you do choose to cast the spell that is queued, it will cast instantly and you will then need to begin casting your next spell. Beyond the one spell you may queue, most offensive spells may only be used while in combat while defensive spells can generally be cast out of combat.
You can also add spells or items to the action bars by dragging them from your Spellbook, bag, bank, or Character Info window to the desired location on an action bar. To remove a spell, simply drag the selected spell off the action bar.