How can the current viewport view be rendered as a preview?
Quickly Previewing the Current View
If you don't need to save the image file but you want a very fast way of previewing the render, position the viewport how you like it and hit ShiftZ. Hit the key combination again to leave the view.
Rendering the Current View
The easiest way to do this is this:
You can read more about rendering in Blender here on the Blender Wiki.