Unlock Train Driver Mode
To access train driving mode, bring up the train window for one of your trains. Make sure the train is fully stopped (red flag icon), and that the train window is the topmost window on the display. Then hold [Insert] while typing driver, then release [Insert]. If you access the stop/go menu on the trains flag icon you should find a new third option in the menu called "Manual". Select the "Manual" option, and the window will change to show a slider control to allow you to control the train. When the slider is at the lowest position, the brakes are fully on. The half way position is when the brakes are fully off but no power is applied. The highest position is for maximum power. Start driving your train, but first make sure it is facing in the correct direction. Be careful so you do not drive it off the end of the track. Then use the mouse pointer to move the control slider up to release the brakes and apply power.
When starting off, start small
Try not to build too fast. Avoid a two track system until you know you have a good income. Just use one train at first. Trains still are not very smart and will take the quickest route to its destination, even if it means going into a dead end. To avoid this, build overhead wires to go to your other station and use a train that needs overhead wires.