In the most casual sense, a renderer is what "takes a picture" of the scene.
A scene is made of objects, light sources, and a camera. The renderer calculates the reflection of light on the objects' surfaces from the perspective of the camera, so that it can decide what color each pixel is in the resulting image.
Objects are made up of a few different data structures: one for physical shape (usually a "mesh" of triangles); one for "texture" (color mapped across the surface); and one for "material" (alters the interaction of light, like adding reflections or transparency).
People don't write the scene data by hand: they use tools to construct each object, often multiple tools for each data structure. Some tools focus on one feature: like ZBrush for "sculpting" a mesh object shape. Other tools can handle every step in the pipeline. For example, Blender can do modeling, rigging, animation, texturing and material definition, rendering, post-processing, and even video editing; and that's leaving out probably 95% of its entire feature set.
If you are interested at all in exploring 3D animation, I recommend downloading Blender. It's free software licensed under GPLv3, and runs well on every major platform. It's incredibly full-featured, and the UI is excellent. Blender is competitive with nearly every 3D digital art tool in existence; particularly for animation and rendering.
A scene is made of objects, light sources, and a camera. The renderer calculates the reflection of light on the objects' surfaces from the perspective of the camera, so that it can decide what color each pixel is in the resulting image.
Objects are made up of a few different data structures: one for physical shape (usually a "mesh" of triangles); one for "texture" (color mapped across the surface); and one for "material" (alters the interaction of light, like adding reflections or transparency).
People don't write the scene data by hand: they use tools to construct each object, often multiple tools for each data structure. Some tools focus on one feature: like ZBrush for "sculpting" a mesh object shape. Other tools can handle every step in the pipeline. For example, Blender can do modeling, rigging, animation, texturing and material definition, rendering, post-processing, and even video editing; and that's leaving out probably 95% of its entire feature set.
If you are interested at all in exploring 3D animation, I recommend downloading Blender. It's free software licensed under GPLv3, and runs well on every major platform. It's incredibly full-featured, and the UI is excellent. Blender is competitive with nearly every 3D digital art tool in existence; particularly for animation and rendering.