Clipping determines which polygons to display. It factors in the location of the camera and the object, with the camera's field-of-view determining how far to the sides you see. Near and far clipping planes determine the nearest and farthest objects to display. Together, the field-of-view and clipping planes enclose a region called the view frustum.

Why does the software bother to define near and far clipping planes? Why not show everything that is in front of you?

There are several reasons. A small polygon that accidentally gets too close to the camera can turn the whole screen a single color, which is very disorienting. The near clipping plane ensures that all rendered polygons are far enough away from the camera to not block too much of the view. The far clipping plane is usually set just beyond the farthest object in the scene to best allow the graphics hardware to calculate the depths of the polygons. But it can also be moved closer to the camera to eliminate some of the more distant elements in the scene. Rendering these far off object would require the same computation as the close object, but contributes much less to the image. When moving the camera interactively in large scenes, bringing the far clipping plane closer can maintain real-time performance.

Setting the near and far clipping planes close to the boundary of your model is a common technique when rendering the pixels of each polygon using z-buffering. Z-buffering entails assigning each point a relative depth between the near and far clipping planes. If that depth is stored as a 32-bit integer and the far clipping plane is too far away, the depths of polygons in the scene will be mapped to only a small part of the 32-bit integer. The net result will be polygons that overlap improperly or get intermingled with nearby polygons. Keeping the view frustum just larger than the bounds of the relevant data helps avoid this problem.

If the image you see is black, it could be because the scene's polygons are outside the view frustum. They could be behind you, too close, too far away, or off to one of the four sides of the frustum.