From the main Trainz menu go into Driver, and down the bottom of the screen click on the word 'Consist'.
A list of rollingstock appears on the right, and double click on any rollingstock you want to operate. This will place the loco into a small bar down the bottom of the screen.
Then click on the word 'map' down the bottom of the screen, select the map from the list on the right, and click on any of the red triangles on the map (these are starter points). Once happy with this, click the green button to get underway.
With Raildriver installed, it should be all the same still, just go about the above process using your mouse.