Why Zip Files?
A Zip file is a compressed file meaning it is used to optimize file size (make it as small as possible), but while still being relatively fast to open.
The other important characteristic of a Zip file is that you can put an entire folder of files or folder with subfolders of files in one file. This is called an archive format and is important because you can only send files, not folders online via websites. This format is often used by me when I want to post many especially small files as one download.
Opening Zip Files
Most Macs and PCs (from about 2005) can open them easily without additional software while iPhones and iPads need iOS 13 or higher for this to be built in. All you do is open the file by clicking it, touching it, via voice assistant or other means and then a new folder or file will appear. The contents are in that new folder or file.
How I Use Zip Files
Currently I use these for my WebP files as I cannot put them in PDFs and they only work in a few e-book (EPUB) viewers, like Apple Books. Another way I currently use the Zip file format is for putting together my vector files in PDF and SVG format for others to edit.