Advanced sharing is an option available for the dashboard editors. You can manage access at the viewer, editor, and group levels simultaneously by choosing it.
To choose the advanced sharing option, use the ‘share' icon first. In the upper right corner of the pop-up window click on the 'cog’ icon to access the Advanced sharing.

Here you can find all users (apart from editors) who have access to view a dashboard and the groups they belong to. Using the '+' icon you can add a new user via email, giving them access to view, share or manage the dashboard and adding them to a certain group.

Here you can see who are the dashboard editors and add them using “+' icon . Note, that editors are not involved in groups.

This tab is for managing group access to the dashboard. Here you can add groups using the '+”icon . The most important feature: you can control which pages will be available to users of a certain group. Tick the pages in the list next to the groups to determine availability.

All users with viewing access have a group membership. If no other group is defined, they belong to the default group. You can’t change the group for the user here - it can be done on the Viewers Tab.