For most windows users you can "right click" on your .zip file and choose "extract". You only need to choose what location to extract to. I usually just choose the default location which is usually the same directory containing the zip file. After you extract your files from the .zip file your digital stamp image files will be located on your computer at the location you extracted to.
There are lots of softwares out there that will unzip (or extract) your zip files. Here is a free one called
jZip - it's a handy utility and you can use it over and over for all of your zip files that you download from the internet.