To create a transformer, go to
DM Electrical 
One Line Devices Transformers
The Transformer dialog box will open as shown below.
Press New. The New dialog box will open as shown below.
Type "T1" for the New Transformer Callout and press OK. Enter the specifications for T1 so they match those shown below. (The specifications that you will need to change are highlighted in yellow in the screen shot below.) Once the specifications match, press Save.
Now you have two panels and a transformer defined in Design Master Electrical. Next, you need to specify how the panels and transformer are connected to each other. Press Exit in the Transformer dialog to return to the drawing.