Use the Drill Up action to access parent data, or use the Drill Down action to access child data.
For example, if you select two Account records and each one has five Contacts, Drill Down will display a grid of the total ten Contacts between the two accounts.
The Default View determines the view seen after Drilling Down or Up. To set the Default View through the Configure drop down, select Manage Views, then check a view as Default.
Here is an example of the parent fields that are available by selecting Drill Up from an Account record: