Back end development is concentrated on how things function and with which logic they are connected. Back-end adds matter to design so they operate together for specific purpose and besides being visually attractive, they can make some actions.
In our conditional case with the car, the back-end builds the whole engine, transmission, suspension, steering, electrics etc. and connects them in their functionalities so they can act together and the car will drive eventually. This is the picture that is hidden from the visual perspective, and to see and feel it, it is necessary to get inside. Based on the back-end, we can understand how functional our product is with its features, how well it operates, and how everything works together. In the car case based on its inner parts and connections, we define the horsepower, engine torque, acceleration, maximum speed, fuel consumption, turning angle, braking etc. based on which we the quality of the car. So the front-end is responsible for how things look, and the back-end how things co-function. There is a popular beginner question which is more important from these two, and I am strongly convinced that they both are equally important. Besides being equally important, in one product, they should also cooperate with each other requirements to represent a quality product. In the car case, for instance, if you have the best engine and the most attractive car body, no one cares about the final car if the engine doesn’t fit under the hood.