This is a technique which allows the rendering of 3D scenes in a 2D fragment shader.
Fractals allow you to generate epic images with only some lines of math & code.
To get started with the math, you can start with Wikipedia: Mandelbrot fractal.
For the mandelbrot set, you just need a
for loop and some complex number knowledge (You will have to google things like "how to take the exponent of a complex number", no need to actually learn anything).
Pro tip: Try using a vec2 to store the complex number, myvec.x will be the real part and myvec.y will be the imaginary part.