Event Groups are a way to categorize your events beyond the standard things like time, type, and location. It allows you to create arbitrary groupings of events, which can then be used by users in searching for events, or by event organizers to limit access to some types of events.
If you go to the Scheduling dropdown in the Convention Tools menu, and then click on Settings, you'll be able to enable event groups. That will then add an Event Groups tab to the Scheduling sub navigation.
Under the new "Event Groups" tab you'll be able to create event groups.
Then you'll have a new section in the event editor where you can assign an event to an event group.
If you create event groups that can limit access by badge type, then you'll have a new section in the badge type editor as well.
And if you add a badge type to the group, you'll be able to set how many tickets in that group the badge holder will be able to buy.
For more information check out this video about event groups: