A backup made by itself. Once a week ERE makes a backup of everything into its own folder "backups" (the backup screen shows where, and Open the folder opens it); the last 4 are kept. Untick "Make a backup of everything by itself once a week" to stop it. Copy one of them somewhere else now and then: a backup on the same computer does not help when that computer is lost. Of the backups made before a restore, the last 5 are kept.
Backup and restore is under Options on the left when the program is in Advanced mode.
Tick what must be in it (everything is ticked to start with; next to each part it says how much there is now), click Make a backup ... and choose where to save it. A backup is one file, with a name that ends in .erebackup. Keep it somewhere other than this computer.
Click Choose a backup file .... The program shows when the backup was made and what is in it. Tick the parts you want back; a part that is not in the file cannot be ticked.
Restoring a part replaces that part. What is in the program now is gone and what is in the backup takes its place. Before anything happens the program says, in red, exactly what will be replaced and what will be lost, for example the downloads made after the backup. Read it, then click Restore ... and answer Yes.
Just before it restores, the program makes a backup of everything as it was and tells you where it saved it (a folder backups next to its database). Restore that file to undo the restore.