The Configuration synchronization form provides a way to interface with the config database table for your Drupal site. When you go to the Export page and create the tarball, Drupal effectively dumps the contents of the config table. Each row represents a configuration entity and will become its own YAML file. The contents of the YAML file represent its database value.

When you import the tarball, Drupal extracts its content. The files are placed in the available CONFIG_SYNC_DIRECTORY directory. The synchronization page parses the configuration entity YAML and provides a difference check against the current site's configuration. Each configuration item can be reviewed, and then all the items can be imported. You cannot choose to selectively import individual items.