In this demonstration, the choke is used when attempting the Kimura arm-lock but your opponent counters.
Put both feet flat on the floor, sit up and grab the opponents right wrist with your left hand.
At this point the opponent knows what you're doing and counters the move by holding his hand behind your back. Sit up and take your right arm round the back of their neck.
Your right hand should be near your stomach (out of view) for a nice tight grip around your opponents neck.
Take your left hand under your opponents chin and grab your right hand, make sure you have a nice tight grip around their neck.
Sit back and cross your feet behind your opponent again putting them back in guard.
Pull your arms up towards yourself and push away with your legs to stretch out your opponent and apply the choke.