If you regularly download files from the web, you'll be familiar with the idea of compressing data to save space, and then decompressing it when it arrives. Common formats for home computers include ZIP and RAR, whilst other less common ones may include ACE, TAR, and TAR.GZ and more. As a Windows user, ZIP and then RAR files are by far the most common.
There are also two very commonly used applications for packing and unpacking these files, called WinZip and WinRAR respectively. You pay for both, and both are superb.
However, there is a free alternative that works as well or better than anything you can spend money on, and this is it. It really has no downside, it does a great job and the price is perfect. It can compress to a higher degree, in some cases, than commercial applications and is as efficient at unpacking files as anything else.
Even if you don't think you have a need for compressing and decompressing (or 'packing' and 'unpacking' or 'archiving' and 'unarchiving') files or folders, you might take a look around your system and see how much clutter there is, stuff that you don't really want to delete, but at the same time, rarely if ever look at. All this can be quickly compressed into archive files, or even one single file, taking up way less space than the originals. It's a useful thing to be able to do. And even more useful, when you can do it for free!