Few things in baseball are as impressive or as devastating as a hard-breaking curveball.  When properly employed, the curveball can dance into the strikezone from such an impossible angle it buckles the batter's knees.  While throwing a curveball can be a true art form, anyone can learn how to do it.  

A curveball begins with the grip.  Place your middle finger on the inside half of the baseball's seam and apply pressure.  Your index finger must then be placed alongside your middle finger.  The two fingers should be touching.  Your ring and little fingers should be placed under the ball, with the ring finger resting against the ball itself.  Ideally, the second knuckle of your ring finger should be on the same seam as your middle finger.  The last piece of the puzzle is thumb placement.  The side of your thumb, and not the pad of the thumb, should be positioned against the ball's seam.

Once the grip is established, it's the hand's movement as it accelerates towards home plate that makes the ball curve.  In contrast to popular belief, throwing a curve doesn't require any snapping or twisting of the wrist.  This will only put more strain on your elbow and shoulder, leading to possible injury.  

Instead, simply throw the ball with the same motion you'd use to pull a blind shut or mimic the Florida State tomahawk chop.  If you're a right-hander, the palm of your hand should be facing first base when you release the ball.  The grip and release will cause the ball to break 12 to six and fall off the table.  The hitters will never stand a chance.