To apply a representation rule to selected features you need to be editing the features. It is convenient to make the feature class whose representation you are editing the only selectable layer in the map. This prevents you from accidentally selecting features from other feature classes.

To do so, right-click the layer in the ArcMap table of contents, point to Selection, then click Make This The Only Selectable Layer.

The next step is to start editing. You'll need the Editor toolbar and the Representations toolbar to edit the representations.

Select some of the buildings in the current view using the Select tool located on the Representation toolbar. Open the Representation Properties dialog box using the Representation Properties button on the Representation toolbar. Click the Representation rule drop down list and choose a rule (in this example the rule is New Buildings) to apply to all the selected buildings. Close the Representation Properties dialog box, save your edits, then stop editing. The features you edited will be drawn using the representation rule you selected.

After you've stopped editing, you can change a representation rule and the features that have that rule will be drawn according to the changed rule. In this example you'll see how to change the rule so the building points will be drawn at a 45 degree angle, and then using an angle stored as an attribute of the features.

To do so, open the layer properties of the layer with the representation. Click the marker rule (in this case, the New Buildings representation rule). On the dialog box for Angle, type “45” for the angle value. Click Apply and move the dialog box to see the changes. Note that all buildings following this representation rule are now angled 45 degrees from horizontal.

You can also set unique angle values for each building.

To do so, click the Display field overrides button. This will make the Angle parameter find its values from within the database. Choose the Angle field from the drop-down list to be the field for the angle parameter, then click OK.