A Zip file is like a directory on your disk. Though it is a single file that can be emailed, copied, etc as one file it has an internal structure that allows many other files to be extracted. Think of it as a ziplock bag. Many Zip files have a ".zip" extension/file type, but not all. The board files in VASL have no file type but are still Zipped. You might see a file called "bdXYZ" for a XYZ module.
Without a utility like 7zip (see below) then rename the file to "bdXYZ.zip". Windows will now allow you to extract the contents.
I use a free utility called 7zip for opening zipped files. The home page is
https://www.7-zip.org/ and the latest versions can be downloaded here:
https://www.7-zip.org/download.html. Just download the appropriate (Windows, 32 or 64 bit, etc) version. Then run the downloaded file (eg 7z1805-x64.exe). I've used versions of 7zip for over a decade, I would not be without it.
With 7zip you can right click on the file and you will see a 7zip line in the pop-up menu. If you follow the 7zip line you will see a submenu with lines like "open archive". The "open archive" will open a window showing the contents of the Zipped file. You can then drag and drop any or all of the contents into where ever you want. You do not have to rename the Zipped file, 7zip will treat any file as a potential Zip file and try to make sense of it as a Zip file. It will either display the contents in a window or give you an error message if it's internal data don't make sense as a Zip file, no harm done though.
You would be surprised how many files are Zip or Zip like in disguise. Many download and install files (.EXE) are really self extracting Zip programs. Just now I downloaded the v18 of 7zip to upgrade my v17 and afterwards out of curiosity right clicked on the v18 install program (7z1805-x64.exe) and by 7zip->Open archive was able to see the contents of the installation.
Though I don't use VASL, I have examined the contents of a few VASL files. Within the VASL download file you can see further files without a file type (IE no .exe, .gif extension). Extract those files using 7zip into a work folder and using 7zip you can then check to see if those extracted files are themselves Zip files containing files like .gif picture files. Potentially you could have many layers of Zip files embedded within other Zip files.