Simply put, a zip file is a compacted version of either a single file or several files.  Windows XP or higher has built-in functionality for creating and opening zip files so you don't need any special software if using those operating systems.

Imagine the following scenario.  You are entering the details for a team's roster and you will be posting a player photo for each player on the team.  To do this, you will need to get each individual player's photo from your computer to the web server so that it can be displayed on the web page.  You could upload each photo one at a time, or you can create a single .zip file containing all the photos.  This has two advantages; 1) The total file size is greatly reduced since every image is compressed in the .zip file (reducing the time it takes to transmit the file), and 2) The time spent uploading images is greatly reduced since you don't need to follow the process for uploading an image multiple times (browse, upload, select, transmit, browse, upload, select, transmit, etc).

Another advantage in using .zip files for uploading is when you have a large single file, converting it to a .zip file before uploading will reduce the time it takes to transmit the file.

The site has been customized to detect when a .zip file has been uploaded and will automatically extract the contents of that file (either a single file or multiple files), and then save those contents to the current folder on the server.  It will also ensure that each file within the .zip file is the correct file type (image, document, etc) based on where you are uploading.  Finally, after saving the contents of the .zip file, it will delete the original .zip file from the server (you will still have it on your computer).