You can change the start time and duration of a clip by clicking
on the clip near the beginning or end of the clip. When you do this,
the Mouse Pointer will change to 
to indicate you can change
the duration or start time. Click and drag to change the start-time or
duration.
Note that you are only restricting the part of the clip that is played out in the presentation, not deleting anything – just drag out the clip end to restore the suppressed part. However, you cannot drag out the ends beyond the original duration of the clip.
