Your Mac comes with an application called Image Capture that is designed, literally, to capture images from devices like cameras and scanners. It has an interface that is easy to navigate and step through when you want to scan a print medium like a document or a book.
Look for another scanning tutorial in two weeks about how to scan using an iPhone or iPad.
If you work through the scan settings carefully, you can successfully capture your desired image. If you rush the process, you might get confused or end up somewhere you didn’t expect.
Let me know if you’re still struggling or need further guidance. I can also offer recommendations if you want to buy a scanner. There are standalone flatbed units, ones combined with a printer, and others designed for speedy document scanning.