A material is a function the engine runs for every pixel, and what it can read is decided by the engine. Here each of those inputs does something you can see. The backdrop is one sprite as big as the screen: its uv times mu.resolution is the pixel it covers, so it draws a line every 40 pixels. The stripe under the title runs on mu.time, which is game time: P pauses the game and the stripe stops with it, and S slows it to a quarter.
Each of the ten models draws one field of a model's FragContext as a colour. A direction (normal, tangent) becomes a colour by taking it from -1..1 to 0..1. worldPos is drawn as bands of the world, so they stay put while the model turns through them, and screen as a checker laid on the screen rather than on the model. viewDir shows as a rim where the surface turns away from the camera. frontFacing needs a shape you can see from behind, so it is a sheet drawn with cull: 'none', green in front and orange behind. carry is written by the model's own vertex hook: each corner is lifted by a wave and hands on how high, and the colour turns to foam on the crests.
Every shader is built with the shader composer, so the same code runs on WebGPU and WebGL2. The full list of names, with their types and the helpers for sprites, models and screen effects, is on the What the engine hands a shader page.