I still dont understand GROUP BY

Here is an explanation with a working example database. The demonstration of the use is particularly helpful.

Your SQL query typically outputs to an array or similar storage method. You then want to use the output is some way, like displaying the information for the client. ORDER BY allows you to sort the data prior to putting it into the array. I am working on a project for a Cub Scout pack. Lets say that I want to list all the scouts in the pack by the highest badge they have completed. I would use order by to output the scouts in that order so I could easily place that data into the PHP for display. I could also sort by scouts that have not completed a certain badge, or by phone number, or by last name, or by first name, or any other data that is in the database. It saves having to manipulate a potentially large array.