The buttons at the top of the Event List window are used to select the types of events that you want to display in the list.
Depending on the situation, you may be interested only in notes, for example, or only program changes or controllers of a particular type. When a button is depressed (on) the event type is displayed; otherwise, it is not.
As you change the filter settings, the list updates to reflect the new choices. Usually there is a slight delay to allow you to select many different choices.