To get started, select your train and stop it in the train window.











Now for our next step, hold down the "Insert" button on your keyboard.
Keep holding it down and type DRIVER (it doesn't have to be uppercase)
Now click on your train window again.
If you hold down the flag, a new option should appear called "Manual". Click this











Once you click this, your train window should look like this.










Now drag the handle on the new Power/Brake tab into the green and your train should move forward.
The further you drag it into the green, the faster your train will go. The further you drag it into the red, the harder your train will brake.
Use the Turn Around button on the right to change the direction of your train.

Congrats! Your in train driving mode.

When driving your train be careful where you speed up, because in train driving mode you can run through red signals, drive off the end of your tracks, or run into other trains and vehicles (which might be a great way to bankrupt your opponents, but I'll let you try that out ;) )

Alright, so now we can drive the train around, but what happens if we hit a switch.










Your train will automatically pick a direction if it comes up to a switch.
However, we can change which track the train will switch onto by clicking on the junction where the tracks meet in the train window when the train is stopped.










As far as I can tell, when you click on the junction, it will cycle through switch alignment.










However, you can better control which switch your train will align to with a signal in the opposite direction.









Even when you cycle through your switch to align to the track with the opposite signal's track, the game will prevent the train from going on that track by taking the signal out of the cycle.