It’s easy to use – just plug your mouthpiece into it and start buzzing in the lower range. Then increase the pitch of your buzz as if playing a scale.
As you ascend higher up the scale you will naturally start to press the mouthpiece harder against your lips. The harder you press, the more you will compress the spring – which in turn will cause the air outlet to begin closing. If you’re pressing too hard, the air outlet closes and the buzz stops because the air cannot escape.
With practice you will learn to ascend higher and higher up the scale without closing off the air escape.
In order to keep the the A.P.E. working as smoothly, you may find it helpful to occasionally clean any debris that might accumulate (pocket lint, etc) between the sliding pieces. A weak detergent solution followed by rinsing with water and drying with a lint free cloth will work fine for this cleaning.
One final tip: be sure to push on the A.P.E. evenly from both sides and in a straight line to ensure smooth sliding operation of the parts.