Options abound nowadays for backing up files. For instance, with the one drive for Microsoft, you can drag and drop a copy of the file you work on your PC. Or when backup is needed because hard drive is fragile and will break from time time, most people just drag and drop the files onto an external disk or USB stick.
A better way exists, however, to perform these simple tasks. I found two backup tools which work great for backing up folders and any changed files, new files or deleted files in a folder. These two program, one for window and another one for Mac, work basically the same. Once I set up the pairs to copy files from one folder on my PC/Mac, and onto another folder on the external hard drive, each time I need to update or backup, I connect the external drive, and hit run. The program will perform the checking and updating. No matter how many files I have changed on my PC/Mac, the files will be updated or backed up on the external hard drive. No select, copy and drag any more.
For Windows, it is Synctoy, made by Microsoft and free to download. Setup is easy and after the installation, the only thing you need is to tell the program which folders on your PC to back up to which folder on the external drive.
For Mac, it is called Silver Keeper made by Lacie, also free. It works basically the same as the Windows program: you pair and run, and the program takes care of the rest.