To back up your files, you can use:
 
•  iCloud Back Up - automatic or manual via your iPad or iPhone's device settings
•  Manual back up of drawings or projects via Files app - connects to iCloud, Adobe Creative Cloud, DropBox, Google Drive and others
•  Direct manual back up to your preferred cloud app
 
We have an illustrated tutorial on backing up your files here - Backing Up Your Drawings.
 
Note that syncing drawings is different than backing up drawings. Syncing mirrors your data across devices, including deletions. Backing up drawings means that your entire device data is backed up and retrievable, so if you've deleted a drawing by accident, you can restore the drawing.