It's all about cloning.

What is cloning? Cloning is the process of producing similar populations of genetically identical individuals. Hahaha it sounds so biology......
Here's two types of cloning which I've learnt.

(A) Clone in :
Using the Clone Stamp Tool and define what to clone in order to clone something that you want. Hold the Option key and click on the nose part and let go the Option key. Clone it on a new area, then brush it across the area gently and you will get a clone in object.

(B) Clone out :

Select an empty area and clone it on the area painted with words, adjust the opacity to make it looks more realistic.

And lastly, how to make a long train?

1. Go to Filter > Vanishing Point and define a perspective. 
2. Look for an area and adjust by pulling it up and down. Drag the selected area all the way back and drag it on the track. 
3. You can use the stamp tool or the Marquee Tool to clone it.
4. For the Marquee Tool, hold the Option key to drag it down and Shift key to lock it on the perspective.

 Before

After

Hope you enjoy cloning. :)