There are a couple effects going on here. Which exact thing are you talking about?
Assuming you’re talking about the parralax-y background and ground making it look like you’re in a cube, I made a similar effect in this game. It’s in Processing, but you can check out the source if you feel like it.
But basically: get out a piece of paper and a pencil and draw a cube where you’re looking into the front side, the back side is your background, and the bottom side is your ground. Draw a few different view angles and the corresponding x,y positions on each side of the cube.