Raymarching is a rendering technique which doesn't rely on meshes, but instead uses a function (conventionally called "Signed Distance Function") that returns the nearest point of the object to a particular sample point, in order to describe an object's geometry.
I started out by looking at code by Inigo Quilez, reverse engineering it until i could understand and adapt his code to render my first objects.
Next I wrote a merge function for two objects that mixes their colors and implemented better lighting.
Then I implemented my own distance function for this object:
I continued to write shaders akin to this, making some of them reactive to audio-data.