1)   What is pkzip25?
Have you ever noticed all of the .zip files out on the internet?  They exist for a reason.  "Zip files" are compressed files.  They cannot be run in zip form.  "What a pain" you say?
For example, you are going on a trip.  You pack your clothes and get to your destination.  Before you can use your clothes you have to unpack them.  "What a pain" you say?  Most people pack their clothes tightly into a suitcase to save space in their car.  Imagine trying to haul every shirt and pair of pants individually out to your car and packing that way.  It takes more space and the process is less organized.
Software compression works the same way.  You take 60 files and compress them into one.  It's cleaner, easier file management.

2)  How do I pack and unpack then?
If this is your first run at zip files, I suggest going to www.winzip.com and downloading the latest version of winzip.  Pkzip25 is a bit more complicated to use.  If you want to learn the 'old school' method please continue reading.  Pkzip25 is a command line based executable.  This means you have to open an MS-DOS prompt from Windows 95/98/2000 (under your programs shortcut group).  Once you have this black screen that says "c:\windows>" you are ready to roll.  First you have to remember where you downloaded "pkzip25.exe".
Let's say you downloaded to "C:\downloads" and you want to pack all the files under a directory called "C:\MyFiles". 
Goto that directory by typing "cd\downloads" and pressing enter.  Zip up that directory by typing "pkzip25 -add c:\myfiles.zip" and pressing enter.  This will take all the files in c:\MyFiles and compress them into a single file called 'myfiles.zip' in c:\.  If you would like to know more, type "pkzip25" in the directory where "pkzip25.exe" is and you will see a help screen.

3)  Why should I use pkzip25.exe instead of Winzip?
I can't tell you what to do.  Winzip is easier and faster.  Pkzip25 helps to extract multiple zips at one time.  If you have to unzip 25 files using Winzip, you have to run Winzip 25 times.  With pkzip25, it only takes one command.