Step 1: Open your hand. Either is fine.

Step 2: Turn your hand upside down and let the palm face upward.

Step 3: Bend the ring finger inward.

Step 4: Clench your favourable middle finger in your palm as well.

Now you are rock. Yet you want metal.
And you are still one step away from it.

Step 5: Use your thumb to grasp the ring finger and middle finger tight.

Step 6: Invert your hand again to find the devil's horn.

Now you are metal. And you feel so metal.

Step 666: Bang you head and the horn together at bpm 666 and scream
"MMMEEETTTAAALLL!!!"
Forever and ever until end of the world. Amen and hail.