Backups are what let you undo a griefing, a bad update or a mod that corrupts chunks. Take them often; they're free to take and you'll be glad of one eventually.
Take a backup
Open the Backups tab and create one. It copies your whole server: worlds, plugins, mods and configs.
Take one before:
- updating Minecraft, your server software, mods or plugins
- adding or removing mods
- resetting a dimension or uploading a world
- any big change to configs
Schedule them
On the Schedules tab, add a scheduled backup, for example every day at a quiet time. Then you always have a recent one without remembering.
Restore a backup
- Open the Backups tab.
- Find the backup from before the problem.
- Restore it.
Restoring replaces the server's files with the backup's. Everything since that backup is lost: builds, inventories, progress. Tell your players before you do it.
If you might want something from the current state, take a backup of it first, so you can go back to it.
Keep a copy yourself
For anything really important, download a copy to your own computer now and then, over SFTP. Stop the server first so the world files are consistent, then copy the world folder.
Restoring just one area
A backup restores the whole server. To fix only a griefed area, tools such as CoreProtect can roll back specific changes without touching everything else. See CoreProtect.
Questions
Do backups include my plugins and mods?
Yes. A backup is the whole server, not just the world.
How many backups should I keep?
At least a few days' worth, so you can go back to before a problem you didn't notice straight away.