a ZIP file (not zippered) is a compressed file. Compressing make the large files smaller to send quicker. You will need to use WinZip or WinRAR to uncompress. Both have a free version, (it just keeps telling you to register).
When you uncompress your file will be it's original size. You will not be able to use this file until uncompressed. If using WinZip or WinRAR is too confusing, ask son to make files "Self-extracting". He should know how.