Step 1.) obtain hold of the apple
Step 2.) contract the muscles in your arm to lift the apple to your mouth (which should be open)
Step 3.) gently close your mouth around the apple, increasing pressure once contact is made. You'll know you've gone far enough when your teeth have a firm hold of the apple.
Step 4.) gently pull your hand and head back in opposite slightly angled directions with the vertex being close to your chin, and the angle opening up until the chunk of apple you have separated breaks free from the whole apple.
Step 5.) repeat steps 2-four as needed.
The proper way to open a box is...