I've been interested in learning shader coding. I love Minecraft and I have several ideas for shaders I'd like to try. I've installed MineForge, coded a few mods. But looking through mods and sample code hasn't given me a good place to start learning and playing with writing shader code, how to hook them in or how to set them up in Minecraft. Is there a good video or sample code or tutorial that can point me at a good starting place for 1.12 shaders? Thanks!

Making vanilla shader packs which do what you're describing (or in general) are incredibly hard. You will need a good background in maths, specifically for 3D vectors, matrices and linear algebra

Here is a good general resources on shaders (they pretty much all work the same way, minecraft just allows usage of certain effects)

• The Book of shaders (general textbook about shaders)
• Minecraft Vanilla shaders guide (r/MinecraftCommand's guide of vanilla shaders)
• General GLSL tutorial (minecraft uses this language)

Once you've finished with the basics and the how to, here are some resources with shader examples

• https://github.com/McTsts/Minecraft-Shaders-Wiki?tab=readme-ov-file (Updated shader repository; may fill gaps in the guide resources above)
• Cloud Wolf's shader playlist (shader examples)

All the minecraft resources are made by people who are basically pioneers for datapacking/command blocking.
If you need more help, dont hesitate to ask the r/MinecraftCommands discord server