Nearly all of the files you download are compressed in some way or another, and this means you need a decompression tool. WinZip is one of the best to use. You can find out what is stored in a file by opening it and reading the documentation before you decide to give it some disk space by decompressing it. WinZip also compress files in the same easy-to-use fashion which can be very useful when you are trying to email a file.