as there is no such thing as "too many resources", here's a selection of interesting online resources
not an online resource yet a must read, find it, read it.
an invaluable resource to understand computational geometry, systems, agents, fractals and so much more... if you're a video person, he is the mastermind behind the coding train
an introduction to computational design with a strong focus on the underlying artistic concepts. the examples use the P5.js library
if you're interested in WebGL & GLSL but still not sure what this means, I warmly recommend going throught these 5 funny and exhaustive books
Gregg has written multiple series of articles to help people understand WebGL & Three.js (and more), the GL examples of this page are based on his tutorials which says it all, go!
Patricio has written a series of articles to help people understand the Shaders, a must read if you're willing to use GLSL
I wanted to have the ability to edit the code and view the result and quickly hacked something but there are plenty of online editors too
this is a collection of demos done by Nicolas Barradeau, it's meant to help newcomers understand the different aspects of creative coding and datavisualization.
the code style is rather quaint, today (2019) one would probably use ES6 classes and tomorrow something different. the idea is to explain the underlying principles so that they can later be used in any language.
it's available on github too :)