I have had a couple of people ask me what a pivot table is so I made a short video that walks you through the basics.
One key bit of information that I left out of the video is that if your underlying data changes, all you have to do is right-click the pivot table and select Refresh.
This will make the pivot table update and display the newest information.

Click on the dog with the movie popcorn to watch the video.

Excel video on pivot tables