Two file compression formats are common: Zip (mainly PCs) and Stuffit (Macs).
(By the way, don't confuse Zip files with Iomega's ZIP drive.)
You might already have one or both capabilities on your computer (see note
If not, there are many programs you can use, and many places to get them.
• WinZip. The most-used .zip program for Windows. Last I checked, it was free to try, about $30 to buy.
• PKZip. From the inventor of the .zip file format, and also popular. Free to try, about $25 to buy.
• BigSpeed Zipper. Does only zip files, but said to be very versatile in other ways. From the people who brought us 100K_Zipper, a very small program that is quick to download and takes little disk space (100K_Zipper is still available at Ziff-Davis ZDnet.) Both are free. As with all free programs, practice safe computing.
• ZipIt. Creates and unzips .zip files on Macs.
• StuffIt Expander, the free decompression program for StuffIt (.sit) files comes
in versions for Mac and Windows. To create .sit files, see StuffIt Lite (older Macs),
StuffIt Deluxe (newer Macs), or
StuffIt for Windows (handles .sit and .zip).
At Ziff-Davis ZDnet and at Tucows, you'll find many other programs that handle these and other compression formats, on various operating systems. NOTE: Some utilities
suites can uncompress files -- try double-clicking on a trusted compressed file
and see what happens. Safe-computing reminder: Although files with a .zip extension
are not themselves dangerous, their contents might be... don't open, run or
double-click on any file if you don't know where it came from or don't
trust its source. ALSO NOTE: Some programs, especially free ones, may run ads or secretly install other programs (such as spyware) on your system. That doesn't seem to be the case with the above, and there are yet other utilities you can get to control such activities, but user beware.