Here is where participants can share resources on various game asset creation tools (ex. Blender for 3D models, GIMP for sprite art, etc.).  This post will focus on 3D tools, as that’s what I’ve had to spend the most time learning. Hopefully others can reply with resources specific to 2D tools such as GIMP and Aseprite, and with resources on music / sound effect creation tools like LMMS and Audacity.

Blender

Most Blender tutorials you’ll find use Blender 2.7 rather than 2.8, which includes a major overhaul in its user interface and numerous other features.  If this is your first time using Blender, it’s probably best to download 2.79 from Blender.org and move to 2.8 when you’re comfortable with it.

BornCG Blender 2.7 playlist, Blender Guru, CG Cookie (subscription required),

Substance Painter/Designer

See Substance Academy.  The Gnomon Workshop has multiple tutorials on Painter & Designer as well.