How do I save JPEG's to my Mac?

Where and how do I save jpeg files on my mac.

Anywhere you want. Photos manages an image library, but if all you are looking for is a folder full of book covers, you can create the folder anywhere in your Home. There is a default folder for Images named "Pictures," but there is nothing special about it.

What do you mean by "how?" Where are the files, now? Just drag them from there into the folder where you want them. Or, drag them into the open Library window in Photos. Or, Import them using the command in the File Menu.

JPEG files (also using the JPG file extension) are one of various sorts of files that can contain images.

Here is a JPEG image (from the linked article) containing a cat.

You probably already have JPEG images stored in your Photos library, but they’re files and can also be stored with the rest of your files. You could place these cover image JOEG files in an album in Photos containing book-related photos, or could store the files in a folder containing the other files related to the books. How you organize your stuff is your choice.

With the books I’ve written, images and examples and the text and the rest are usually all stored in a folder of related “stuff” for that book, with that folder created within my Documents folder.

See the following links for more info on using a Mac.

If you want to learn a little more about macOS: macOS User Guide - Apple Support

Many Apple stores have classes that can help with the jargon and the concepts: Today at Apple - Apple