To make a backup, you just need to go to your data folder and copy everything in the location where you want to store your backups (another local folder, an external hard drive or even a cloud storage like Google Drive or Dropbox).
When you need to restore a backup, simply copy from your backup folder to your Foundry data folder and overwrite everything.
This video by Encounter Library is a pretty good guide to help setup backups:
https://youtu.be/OmbxMmqNNXU
