Tucked away in Apple's OS X software is a built-in compression app that the Finder uses for zipping and unzipping files and folders. When you download files from the web, this built-in app does the heavy lifting and decompresses the files for you.
Courtesy of Apple
You can also use the built-in compression capabilities for your own purposes. If you would like to compress a bunch of photos to send off to family, this is the tool to use. Compressed files take less time to send and receive, and the zip format used by the Mac is compatible with most OSes, including Windows, so the pictures you send can be viewed by just about anyone. It's a fast and easy way to share holiday photos with far-flung friends and family.
For more information about using your Mac's compression app, take a look at: