A class three lever has the force and weight on the same side of the pivot, with the force closer to the pivot.

Example:

  Weight   Force
    \/       \/
  _______________________
 (_______________________)
                    /^\

                   Pivot

Class three levers are used to give a distance or speed advantage.

Your elbow and forearm is an example of this, as smartalix astutely pointed out to me. The pivot is your elbow, the force is provided by your muscles, and the weight is whatever is in your hand.