You must create a class for each different label by first adding a new class with the Add button. The user creates a name for each class. After the class name is assigned, use the ‘SQL Query’ button to define the specific criteria for the class. (This SQL Query dialog works the same as all other query dialogs within ArcMap.)
There will be a class designated as ‘Default’, which you may want to turn off by un-checking the box ‘Label features in this class’ to avoid multiple labels for each feature.