When displaying results, sometimes certain results are related by a common data element. An obvious example might be "State", where you might want all results in a certain state to be displayed under a state-level heading as shown below.

To enable grouping, under Filter & Sort, choose the field to Group on under Field Sorting, and be sure to check the Group checkbox as shown:

At this stage you must Save the interface to continue.

Once saved, you will see a new template container called Group available in the Results > List as shown below

Any fields added to this group will be displayed in the Group heading. If the value added to the group changes more often than the value in the chosen group, the first value in the set of results that match the group will be used.