You really need to read section 8 - INTRODUCTION TO SURVEYOR in the manual
But for now, run TS12 and click the start button.
Now click routes and pick a route you want the Duchess to run on, lets say the ECML route.
So click on the ECML kings-cross - Newcastle route then click the create session button.
Now pick a section of track you would like to run the train from, like a siding or something.
Select the Trains tab (F7) from the tab Panel.
Now scroll down and select BR Duchess Green from the list of available items.
Click on the add button (+) in the same tab menu.
point the cursor at the piece of track you want the train on and left click the mouse.
Now do the same thing with the tender and carriages.
Now you need a driver.
At the top left of the screen there are four round buttons, you want the one with a white square which says edit session rules.
Click on the driver edit square then click the edit button for the driver menu.
you should have a driver already selected for you the first time, but if you add more trains you will need to add them your self, and select the vehicle to go with the driver.
You can now tick the boxes, to get back to the main screen.
Now click the main menu box (top left) and select Save As...
Select the Save Session button and give it a name.
At last you can run the session with the quick drive button (top left round button with white triangle, or Ctrl+F2).