Choking is a very essential acoustic guitar and electric guitar technique. It is one where you stop the sound from continuing. In other words you are able to control the time of the vibrations of the strings. Choking is one of the basic techniques to be learnt .It is done by slightly removing the pressure from your left hand fingers .For this you have to be good at your chords .You must know your chords well, i.e. you should not take time to place your fingers on the fret board. A demonstrational video is given below on an electric guitar. The same concept is applicable for an acoustic guitar too.