The Backup Repository is a location on your machine that stores all of your User's backups. Learn how to create it and how it is structured in the background.
Choose a drive/partition with sufficient available space, then browse to this location when creating a user.
When Adding a User, specify a directory for your Repository location, then Syncrify will create the folder at the specified location.
The subfolders in the Repository are automatically created when a user runs a backup. See Admin, Users, & Profiles for information on the differences between a User and a Profile.