Every Mac user should be backing up the files on their Mac. The easiest way to do this is to use Time Machine, which is part of macOS. You can get a cheap external hard drive and start doing this today. Time Machine is simple and automatic and can save you from disasters, as long as you start using it.
Time Machine is the part of macOS that allows you to easily back up your Mac to an external or networked hard drive. Here are some of the most asked questions about Time Machine, such as what size hard drive do you need, can you exclude files from the backup, and how do you restore files from the backup.
When you use Time Machine to back up your Mac, you not only get a complete backup of everything, but also a history of files that includes deleted or modified files. You can recover a file you have deleted even if many backups have occurred since you deleted the file. Practice this technique so you know how to use it before you need it.