Beating Voldermort is actually quite easy.
There are two battle phases for the battle with Voldermort.
The first phase is quite easy, even if it is your first time battling Voldermort.

Okay now lets cut to the chase so you can defeat Voldermort in a short amount of time.
In the first phase there will be exactly twelve gravestones. When Voldermort is using his magic, Hide behind one of these gravestone.But BEWARE some of his magic shots do destroy the graveston that you are hiding behinde.
When he is standing still you shoot him with you magic. Continue this untill you defeat his first phase.

Okay now that you are ready for the second phase I will fill you in on the info of the phase.
The second phase should be where one of your magic shots goes against one of his magic shots. The there should be a combination of buttons displayed at the bottom of your screen.
Press those random combination of buttons like you would in a dancing game.

You now should have finshed the game.