What aspect of the shader nodes confuses you? The nodes are basically just steps in a flowchart. The data being processed and operations used to manipulate that data are all described as nodes that you link together in the order the operations should be done (from left to right).
For example, to adjust the hue on a texture that a shader is using, you add a hue node between the texture node and the color input of the shader. Just remember that there is a difference between the image output (yellow dot) and the shader output (green dot). Those shaders describe how the ray should interact with the object when the scene is rendered, so you wouldn’t be able to adjust the hue after they are used in the node tree (you can adjust the hue of a image, but you can’t adjust the hue of a math equation). This is why eevee has to use the shader to rgb node in order to adjust the textures used for the shadows of an object. That node converts the rendered result into an image that can be feed back into the shader.
Node systems are flexible. You can also use them to recreate how image layers in 2d painting software work:
And you might also find this site to be helpful:
https://blendernpr.org/learning-resources/