Go to the little cabin you see at the far end of the screen. Basically go to the right of the ladder that leads to the top of the bridge.
Or maybe you mean that you don't know how to get the train started? If that's the case then there's a pencil at the front of the RV. It's kinda hard to see. It's in the cup/drink holder to the right of the steering wheel.
You need this pencil I assume. If you need more clues, let me know.
Unlike the other guy I don;t assume you're an idiot. You'll have to send the little girl over the top of the gate once you see the keys on the other side.
I didn't assume he's an idiot. Please don't put words in my mouth. At first, when I reached this part, I too was like WTF where do I go. I figured it out though. The game is not fun if you know exactly where to go and what to do so I left out that part for him to figure out.
He seemss to be at the area where you have to find something (keeping it spoiler free) to bring the tanker down.
EDIT = If anything, your post assumes he's an idiot because there is no other point where you can click on in that area (the forklift is broken and the door is locked, that leaves the only other point that you can interact with)