Thanks - I started in QBasic when I was maybe 15 and made a solid volume in Mode 13H. It ran at about about 1 frame per minute.

I am mostly self taught, which is good and bad. Bad, because it takes way longer, good because you learn how to derive solutions yourself and learn why things work the way they do. My recommendation is to either start with a set of OpenGL/DirectX tutorials or just get some pixels on the screen any way possible, and build a software renderer from there -- that is if you want to learn. If you want to make a game, your best bet is to use an existing engine, although I'm hardly a shining example of that.

Great advice, thanks. Are there any good resources specifically for volumetric, cube or voxel rendering? Is it completely different than polygons?

This may not be exactly what you're looking for, but it made some of the concepts "click" for me.

https://youtu.be/gNZtx3ijjpo (three parts).