Navigation:

Use the arrow buttons located at the upper-left of the map to move the map in that direction.

Alternately, you can click and drag the map to move in any desired direction.

Magnification:

Zoom in or out using the plus and minus buttons under the arrows. The slider between the plus and minus buttons can be moved to dynamically magnify the map.

Centering:

Click the button in the center of the arrow buttons to center the map on the original coordinates.

Alternately, you can double-click the map at any point; the map will automatically center on that point.
Google Map Demo