Many of the files you may want to download from the internet are compressed files. There are a variety of compression formats used. The compressed files on this web site use the "ZIP" file format. A file, such as "xyz.zip" is a compressed file. The compression makes the file smaller, which has the benefit of using less storage space on internet servers and taking less time for you to download to your computer.
Once you have downloaded the file, however, you will have to uncompress it to get the files included back to their original, uncompressed, format. Compressing a file is sometimes referred to as "zipping the file" and uncompressing it as "unzipping". One of the most popular zip programs is called WinZIP and that is used to compress and to uncompress files.
This feature is so prevalent on the internet that the process of zipping and unzipping has also been built into recent operating systems and some of the internet browsers. On my Mac, for examples, if I want to compress a folder "ExFiles", I merely select the folder and then, with a right mouse click, choose the option to "Compress ExFIles" and the system automatically creates a file called "ExFiles.zip". On my Windows XP computer, I right-click on a folder and "WinZip" is one of the available options for that folder.
Another advantage of zipping being so prevalent is that I don't have to actually draft lessons myself. There are plenty already available on the internet and I will simply provide some pointers here so that, if you are new to the whole process of file compression, you can learn all you need to know. Many of the links below will also provide links to programs you can download to zip or unzip your own files. These are not necessarily the "best" links out there, but they will get you started.
UCI|EEE Lessons on Zip files -- how to zip or unzip a file on a variety of different platforms.
ZIP (file format) - this article, from Wikipedia, the free encyclopedia, will provide technical information on the zip file format and it's history, competing compression formats, and links to additional references.
Windows 7 Tutorial: How to Extract Zip Files - Here is a short video showing how to unzip a file in Windows.
WinZip - home page for WinZIP, the Compression Utility for Windows. This is no longer a free utility. Current version is WinZIP 14.5 which is $29.95.
The FreeSite.com - you will find several free utility programs here that you can use to zip and unzip files.
How to zip & unzip files - a short tutorial from Mantex. Includes step-by-step instructions for downloading, unzipping, and zipping files.