2D in a 3D space

Hi, this is just a general question about implementing 2D art in a 3D space. I would like to make a game with a flat paralaxing background like the game Night in the Woods which was made with Unity. For that game did they have to build the whole town like a 3d model and just texture it in a way that make it look 3D or is there something within the unity engine that makes using 2D art possible for a semi platformer. Also how does implementing a flat background work? Sorry I'm very new to the game making community and just cant find any videos or articles talking about how this works. Thanks for the help.

 

https://unity3d.com/learn/tutorials/s/2d-game-creation
https://unity3d.com/learn/tutorials/s/2d-game-kit

 

Unity has built in support for 2D game development. You can also create a completely 3D game, place all your objects on a specific axis and constrain everything to that axis to get 2D like gameplay from a completely 3D environment.