The rule in plain words
Three copies means the working copy plus two backups. Two types of storage means not putting every copy on the same kind of device, because drives of the same type can fail in similar ways.
One copy off-site means somewhere other than your home or studio, such as a cloud account or a drive kept at a relative's house. A fire, flood or burglary then cannot take everything at once.
A simple setup for a creator
Copy one is the folder on your laptop or desktop where you edit. Copy two is an external drive that you plug in once a week. Copy three is a cloud storage account that syncs or uploads your finished exports.
Your phone does not count as a backup. It is the place videos are born, and it is also the device most likely to be dropped, lost or reset.
Decide what goes into each copy
Raw footage takes the most space and may not need three copies forever. Final edits, thumbnails, captions and your content log are small and irreplaceable, so give them full 3-2-1 protection.
A practical split is: finished videos and records everywhere, raw clips on the computer and the external drive only, then delete raw clips you will never reuse after a few months.
Make it a habit, then test it
Put a weekly reminder in your calendar to plug in the drive and check that the cloud upload finished. Ten minutes a week is all it takes.
Every few months, pick three random videos and open them from each backup. A backup you have never restored from is only a hope, and testing is how you find a problem while you still have the originals.
Frequently asked questions
Is cloud sync alone enough?
Sync is helpful but risky on its own, because deleting a file on one device can delete it everywhere. Keep at least one copy that is not a live mirror, such as an external drive you update and unplug.
Do I need expensive equipment?
No. A regular external drive and an entry-level cloud plan are enough to start, and you can grow storage as your library grows.