To use Groups to limit users to venues requires 2 things:
A User Group needs to be created in Users > Groups
The Venue needs to be setup in Concierge > Manage Venues
To create the User Group, go to Users > Groups and create a Group.
Once the Group is created we then need to assign Users. The Fastest way to do this is to bulk select users under users and assign them to the group
Once all the Users have been added to the User Group, the next step is to either create the Venue or Edit an existing Venue. This is done in Concierge > Manage Venues
Fill out the appropriate details and then in Authorisation, limit the target audience to be the User Group.