How should you actually back up your files?

The standard framework is 3-2-1: keep three copies of your data, store them on at least two different types of media, and keep one copy off-site. In practice for a household that means the working copy on your computer, a local backup to an external drive or network device, and an off-site copy through a backup service or a drive stored elsewhere. The reason for the redundancy is that the failure modes are different: drive failure takes the local copy, theft or fire takes everything in the building, and human error or ransomware takes whatever is connected.

The most common mistake is treating file sync for backup. Services that mirror a folder across devices propagate every change, including deletions and encryption by ransomware, to every copy within seconds. That is a convenience feature, not a safety net. Real backup software keeps versioned history so you can retrieve a file as it existed before the damage, and it retains deleted files for a defined period. If your sync service offers version history and a recycle bin, that closes part of the gap, but the retention window is usually short and it does not protect against account compromise.

What to actually set up. Turn on the operating system's built-in backup to an external drive, which is free and automatic on both major platforms. Add a cloud backup service for the off-site copy, priced at a few dollars a month for a personal machine. Include your phone, which for most people holds the photographs that are genuinely irreplaceable. Then do the step everyone skips: test a restore. A backup you have never restored from is a hypothesis, and discovering it was silently failing for eight months at the moment you need it is the standard way this ends. Check it once or twice a year by recovering a file, and keep at least one copy disconnected when not in use, since anything permanently mounted is reachable by anything that reaches your computer.