How important is "unzipping"?

Programs like Winzip, how important are they?

And what do they do exactly, and why doesn't the OS come with it?

Read the winzip faq. Or type it into google. Because I really can't be fucked explaining what has already been explained a billion times.

If you have windows XP+ you don't have to worry about winzip, because a zipping utility is built into the operating system.

A zipping utility basically compresses the file size of one or more files, allowing for faster downloads/uploads, and takes less space on drives.

In lamen speak:

This is just an example, and my numbers may not represent the actual ones

File A = 1.5mb
File B = 1.5mb
File C = 1.5 mb
Total = 4.5mb

If you take these files and "zip" them, the zipped file will be 3mb. You then can email this 3mb file to a friend, they can unzip it and they will have the 3 individual files installed on their system or whatever.

If you download files (games,music, etc..) off the Internet, it is a good idea to have a zipping utility.

A very simplistic explanation. Depending on the file type and the compression algorithm already used on the file, compression can be as little as 1% and as much as 99% for something like a Word/Text document.

Zip archive's are also useful for grouping a lot of files together into one .zip file for transfer, instead of a whole lot of individual files.