Although WebGL is often thought of as a comprehensive 3D API, it is, in reality, just a rasterization engine. It draws points, lines, and triangles based on the code you supply. Getting WebGL to do anything else requires you to provide code to use points, lines, and triangles to accomplish your task.

WebGL runs on the GPU on your computer. As such, you need to provide code that runs on that GPU. The code should be provided in the form of pairs of functions. Those two functions are known as the vertex shader and fragment shader, and they are each written in a very strictly-typed C/C++-like language called GLSL (GL Shader Language). Together, they are called a program.