If you're using the Concealer Pen, you can press the button on the end of the pen until you see concealer (this may take a few clicks the first time you use it) and directly apply the product to any areas you would like to cover. If you're using the concealer pot, simply use your (clean!) finger or a sponge to get a little bit out of the pack.
Then, use your fingers or a sponge to gently blend the product onto your skin. Use a tapping motion rather than a dragging motion. Remember, a little goes a long way and you can always add more if needed.