Events group are a simple way to keep your events organized. For instance, you might have some events that will be related to Social Media, Aquisition, Conversion, Newsletter campaigns, etc.
By default, the General category is created for you. You can create new group by clicking on New group as shown below.
You can always check what event is actually doing by clicking on the event name in the left column as shown below.
You will get a quick preview of how many times this event was triggered during the past few days and can always update it if needed by scrolling below the chart.