The cutter should be gripped similarly to the two-seam fastball, but both fingers should hug the outside thread of the inside seam. The finger pressure should be tight, with the middle finger getting the most amount of pressure. The thumb should be on the opposite thread underneath the ball with slightly tight pressure, and should be pointing out. This type of pressure gives the ball more of a slider type feel. The ball is thrown by spinning it off the middle and index fingers, but the wrist action should mirror a fastball.
The result should be a straight path that veers away from the hand side at the very last moment. Simple tweaks in finger pressure and the amount of release your fingers use dictate the amount of slicing action on the ball.
If a pitcher has strong and long fingers, this pitch can have nasty lateral movement and will be almost undetectable until it is too late for the batter to pick it up. It is the reason why pitchers like Mariano Rivera can make a long career with the cutter alone.