To add a state to your DES, make sure you have Selection mode enabled.
Enable the type of state you wish to add by clicking on it in the left pane.
Next click in the DES editor workspace where you wish to place the state. This will open the DES State Editor dialog box.
Enter the state name and alias in the text boxes. If you selected the wrong type of state you can change it by clicking the checkboxes for the initial and marked properties. Click OK and your new state will be added to the DES. You will notice your new state listed in the states pane.