This is the quickest and most pain free way of amplifying your acoustic guitar. They are designed to be stuck on to your acoustic guitar with the adhesive pads included to then be run directly into an amplifier (6.35mm version), or a onboard preamp (3.5mm version).
These pickups are piezoelectric crystals in a metal case, when piezoelectric crystals are subject to vibration, they emit a small current in the same frequency. When they are in physical contact with your guitar, they will 'sense' the notes being played and then will create a corresponding electric signal.
The piezos can be placed anywhere on the body of the instrument for different tones. They are commonly put near the bridge for the maximum volume.
6.35mm jack version has a 3 metre cable.