Ask HN: Getting started with WebGL?

I've recently noticed a lot of websites make use of WebGL in one way or another. Working as a professional, freelance web developer I would love to add WebGL to my skillset. However, most tutorials I find don't go in depth. At most, you get to render a cube on the screen. I would love to be able to get past that point and more complex things, but I don't have an extensive background in 3D programming, math, etc. How do I get started? One of my favourite websites I've recently come across is: minglabs.com. I would like to be able to build something in the same vein someday.