You mean just to pack the file if so,then just run your mouse pointer over the file you want to pack,then click right or left mouse button depending if your right or left handed and a pop up menu will show and you should see some winrar icons in that menu named.
Add to archive.. Add to "your file`s name" Compress and e-mail.. Compress to "your file`s name" and e-mail.
Just choose one of the first two and click on one of them and a winrar window will open and just press the ok button and it will pack the file for you and when done will be in the same directory or you can make changes to packing before you press the ok button if you like also.
The other two choices are if you want to pack and e-mail them right away.This is how i do it and it works great! Hope info helps.
if you want to adjust how it's compressed, choose add to archive... and in there on the left side there's a drop down menu, choose store if you just want to have a bunch of files in 1 archive, or choose best if you want to make the file's as small as possible..
Most lkely a dummy file of some sort or more than one inside of that file (i`m thinking) as this might account for the smaller size you are describing,and once packed you would have to unpack it before you could burn the file.But does work good for storing them to save pc hdd space. To get the best compression though choose best as MKE has mentioned in his post on the procedure.