Use the cross-hairs to select the location(s) for which you want to set the constraint.
Select the analysis type for which this constraint is being set.
Click
Apply.
An appropriate constraint symbol will be displayed at each node you have constrained.
Click
Close to close the dialog.
Note: Now that you have successfully set the model constraint(s) in order to prevent rigid body motion, you can now apply the required load(s) to the model.