Here are four helpful videos highlighting the gradebook in Moodle 2.3. Each video builds upon the last so watching them in order will be great. The gradebook functionality is covered from the basics to the advanced (though the narrator does suggest that Excel is a great way to export and import within Moodle, at least for those extra complicated gradebooks).
Check out the playlist here: http://www.youtube.com/playlist?list=PLPO9soATEE9PckVjW7GZcL7XLEnmLHfhC
For more great videos by Humboldt State University visit: http://www.youtube.com/user/HSUInfoTechServices