Enable analytics on your gallery to track visitors and actions.
In Round Settings > Application Gallery check "Enable Analytics" to use this feature.
This will add a link under Tools for Application Gallery Analytics.
The follow Reports will be available:
Who actually visited/clicked on each entry
User Clicked on Join Button
This is for events where the Join Button is the live session
User Watched Video
This is when someone watches the recording of the past event
User Clicked on External Link
This is when someone clicked on any link within the entry.
Under the Charts tab you'll be able to see this same information displayed across various graphs.