The clipping plane is a good example of an object with manipulators. A clipping plane can be activated with the View→Clipping Plane
menu. After activation the clipping plane object appears and shows
seven obvious manipulators as little boxes: One on each end of its three
coordinate axes and one on the center of the plane normal axis. There
are four more that are not as obvious: The plane itself and the thin
part of the three axis objects.

Scaling

To scale the object click with the left mouse
button on the box manipulators at the end of the axes and pull them back
and forth. Depending on the object the manipulators work independently
or synchronously.

Out of plane shifting

To shift the object along its
normal vector, pull the long box on the center of an axis with the left
mouse button. For the clipping plane there is only one manipulator along
the normal vector.

In plane shifting

To move the center of the clipping plane, click on the plane object and pull it to the desired location.

Rotation

Clicking on the thin part of the axes puts the manipulator in rotation mode.