Have you ever lost your files? I can tell you from experience that it is a gut sickening experience. All it takes is a sudden hard drive failure to lose everything, even with a new computer. I had a top of the line HP business desktop that suffered a hard drive failure only 1 month after purchase. Luckily I had already learned to create backups.
A great majority of us tend to procrastinate this backup process. It is not an issue of "IF my computer hard drive crashes", but "WHEN it crashes". Storage devices wear out or quickly go "bad". They should probably be replaced fairly often, or at least every few years.
These "clouds" are basically large "server farms" where data can be securely held and kept safely backed up.
There are many “Clouds” to choose from with probably the most common being Dropbox, Google Drive, Microsoft OneDrive, and Apple iCloud Drive, however there are many others as well. The cost is minimal, 99 cents/month for 100gb of storage, and on up the tiers to $10/month for 2 terabytes. Each service will vary, so you will need to explore what plans they have.
Having your files stored in a "Cloud" offers you a way to keep all your files synchronized across multiple devices (iPads or tablets, Laptops, Desktops, etc). When a file is uploaded or changed on one device, all the devices connected to your "cloud account" will then be updated to reflect the current file changes.
Most of the major "Cloud Drives" offer a desktop app that will install and integrate into your desktop browser (File Explorer in Windows or Finder on Macs). This allows you to organize, move files, or create folders in your "cloud drive", just as you would do with any of your files on your hard drive.
A file in the "cloud" is available anywhere you may be, such as at the Family History Library, "on the road traveling", and so on, as long as you have internet of course.
What if your computer hard drive suddenly dies? Don't worry, your files are still stored on your cloud drive. Replace your hard drive, reinstall your "cloud's" desktop app, and the files will download back to your desktop. This should NOT be your only backup strategy though!!