No problem, but it may help seeing the associated images which also have tips, here is how to do it...
I'm pleased to say it is really easy, here are the Power Functions parts required:
- Battery box (88000 batteries, or 8878+45517 for mains power although please double-check country equivalent if not UK)
- 8884 IR Receiver
- 88002 Train Motor
- 8879 Controller
- 8870 lights + 4 Pick A Brick parts for the lights (optional!)
- Track!
Simply remove the wheel base from the engine tender, the black plate top of it and the fireplace from the engine.
The train motor becomes the base of the tender as shown. Re-add the 4 dark grey 2x1 bricks from the tender to the base to act as supports for the rest of the tender assembly. Also add the engine and passenger car couplings to the train motor. Place your battery box in the tender and the IR Receiver in the engine cab.
For the power, connect your IR Receiver to your battery box. Your IR Receiver has 2 ports, add the train motor's plug to one and the optional lights to the other.
You're good to go!