Use the spike on the end to punch a hole roughly in the centre of the end of the can, move the handle through 90 degrees until the cutter touches the end of the can, move it out to the rim, apply pressure to force the cutter through the end (you now have two holes, one in the centre is the pivot, the other is the start of the cut) - grasp can firmly in left hand, pull handle toward you with the right hand and it will start to cut as the cutter follows the outer rim of the end - keep going until back to starting point and the end should come away, held by the centre spike...
Did they make these with double edged blades for left or right hand use??