Gather everything together, for my peaks I use Wilton tip 2D, but you can use anything you like, or just clip a hole in the bottom of you're bag.
Fill pastry bag half way 3/4 full. Never over fill the bag, it will just fall out the back end and make a mess.
Hold you're bag at a 45 degree angle and rotate the cupcake, holding the bag in the same place. The requires both hands which is why there are no photos of it being done the whole time. Twist and bring it in slowly until you reach the middle.
It should like this when you are done step 3.
Do that same thing on the next level, but leave a ring of the bottom layer showing.
It should look like this when its done.
Yay :) You finished you're cupcake. Now sprinkle away.