How do you use zip files?

Zip files have limited uses:

1. To compress very large files for transfer over the Internet.
2. To keep files for long term storage.
3. To make data easily transferrable across different networks.
4. For basic email transfers.

They are as safe as they have always been.

The algorithms are fairly complex ways of substituting one character for characters that are often repeated. This results in a smaller, i.e., compressed file.

Zipping an image file should have no effect on image quality, as the image data is not actually changed.

Note that there's very little point in zipping a folder full of images, unless the images are not a compressed file type. You can't compress data that is already compressed - in fact, trying to do so often increases the file size - and JPEG images, for example, are already compressed.

For the most part, you don't need to use zip at all. I absolutely DO NOT recommend storing your files and/or folders on the hard drive in compressed form as a space-saving measure. It doesn't save enough space to be worth the time needed to compress files large enough to warrant it on a modern drive. Accessing zipped files is a pain, too, since you basically have to decompress the whole thing in order to access a file inside a zip file.

Zip becomes useful if you need to attach a large number of files to an e-mail message (zip the files, then attach the single zip file) or want to create an archive of multiple files to download from a web site through a single link. In other words, in situations where you need to transmit many files over the internet, especially where Windows users may be involved, zipping files can be either important or a convenience.

Yeah, modern drives are large and cheap enough that going to inconvenient, time-wasting measures to save space is not worthwhile. You'd be better off to just buy a larger drive.

Images typically don't compress much if at all because of the nature of the datafile. Yes, it is OK to compress a folder of mixed filetypes. Image quality is not affected. All files must be decompressed - unzipped - before they can be used in any way. That simply returns them to the original state.