3D rendering is like making pictures of things that don't exist or things that are too difficult to take pictures of. You know how you can use colors, pencils and paper to draw a picture? Imagine doing that but using computers, special software and super smart math.
The computer creates a 3D model of the thing you want to make a picture of. This model is like a digital copy of the thing, with height, width and depth. The computer then breaks down the model into its individual parts, called polygons. Think of it like breaking down a toy car into its tires, wheels, body and so on.
Once the computer has all the polygons, it creates a virtual camera that looks at the model from a specific angle. The computer then figures out how the light would reflect off each polygon and what the colors and shadows on each polygon would look like. It's like shining a flashlight on a toy car and seeing how the light reflects off of it.
Once the computer has figured all of that out, it takes all of the individual polygons and combines them into one big picture- this is called rendering. This picture can then be viewed on a computer screen, printed out or even used in movies and video games.
Excitingly, the process can take a long time- sometimes even hours or days- for the computer to render a complex 3D image with lots of details. It's a bit like baking the tastiest cake: even though it takes a while to make, the end result is worth the wait!