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What is a .ZIP file?

A .ZIP file is a single compressed file containing one or more other files.

You would want to ZIP a file to cut down on the amount of space that file takes up on your hard drive.  You can ZIP almost any file but some files are already compressed, such as .MP3 and .JPG files, so zipping them saves very little space.  Keep in mind that you cannot use a file while it is still zipped.  You have to extract the file or files before you can use them.  MP3 and JPG files are still usable in their compressed form.   Sound & picture quality is degraded and can never be recovered when using MP3 or JPG compression methods.  That is not the case with ZIP files.  The contents of a ZIP file will uncompress to it's original state.  Sometimes you can run files from within a .ZIP file but it's best to extract all it's contents first to avoid errors.

MP3 files are compressed WAV files.  JPG files are compressed BMP files.  You might still want to ZIP your JPG files so that you can keep them all together when you email pictures to someone but ZIPPING files that are already compressed will not save much space.

Say you had 20 picture files on your computer that you wanted to send to someone.  Instead of attaching each file individually in your email you could ZIP them first and attach the single .ZIP file you created.  The new file you create should end in .ZIP and would contain all 20 pictures you wanted to email.  If you take away the .ZIP extension another user may not know how top open the file.  The .ZIP file extension is what Windows uses to decide which program should be used to deal with the file.  The same way .JPG identifies a picture file & .WAV identifies an audio file.

I only use upper case file extensions in this document to stress the importance of knowing & identifying different kinds of files.  Windows doesn't care about upper case & lower case file names.  PICTURES.ZIP & pictures.zip are the same file.