There are several options on ways to backup your PC. You could use a third party utility, copy the files yourself or use Windows Backup.
Reasons to backup are that if anything happens to your computer or to your data, you can still get it back from some point in time, depending on how often you backup. The data could be damaged by malware or the drive it is stored on could start failing or have a bad spot or the building you have the computer in could be severely damaged by fire, storm, etc.
You want to keep your backup separate from your computer and you do not want to leave your backup plugged in or connected to the computer. If you were to get hit by ransomware, many varieties of it now delete stuff not just on the main hard drive but all storage devices attached. Also if something happened to the building where the computer is and the backup is there also, then you lost the backup.
You could get a third party backup utility which some are available as freeware and some cost money. I have not tried many of these. I know some people who use Acronis Imager to make a backup and are happy with it. It makes an image of your hard drive and stores it on DVD.
The Windows Backup program will constantly make a copy of files on your computer to a different location and you choose whether every 15 minutes or a longer period up to once a day. It wants to use an external drive and you will need several to be rotating if you follow my above suggestion of keep backup off-site. Most organizations backup one a day.
The third way which is part of what I do is to regularly copy all your data files (pictures, documents, etc) to an external drive. I actually do not copy all the files after the first time but copy all the folders I have made any changes in since I last backed up. I normally backup my computer every Thursday night and Sunday night. That way if something does happen to my computer I only lost back to last Thursday or Sunday. It also makes the copies quicker as just folders with changes copied. I could add a setting to just do files with changes but I do not. To do this I open the drive I am backing up in File Explorer and then open another copy of the File Explorer and have drive I will copy to showing but not open. I then drag folders from the first folder to the backup drive in the second window. When it says the file already exists I choose to replace all that already exist.
The fourth way is to copy your files to storage you have on the cloud. Many people have a large amount of space on Google Drive or Microsoft’s One Drive. Then copy your data to there similar to how I described in my third method. I use both of these sometimes, but the place I backup my pictures to besides the external drive twice a week, is to Shutterfly. They allow you store unlimited pictures there for free (and you can share or not share). I probably have over 100,000 pictures there, they said unlimited and I am trying to find what number that is lol. You can view almost all my pictures there at dwightwatt.shutterfly.com although a few are in private folders for various reasons. There are others that will give you space for pictures too, but Shutterfly has since about 1999 for me for free and has taken over some of the others like Kodak and Seattle Filmworks.
The major points were, backup regularly somewhere, and keep the backup at a separate location (at least a different building).