Hey mmichhhcim,
You are not alone, using nodes in the shader editor can be really confusing for pretty much everyone when learning. Some more advanced users will tell you they are not entirely sure what's going on, but they have an understanding of the different types of nodes and have an idea of what they do. Most of the time its trial and error, given enough time this is less obvious.
My advice would be to be patient, watch the course from beginning to end more than once. The first time you watch the lessons, do exactly that, just watch. When you watch and follow along the next time, you will find more things will make sense.
Also, I recommend watching theΒ fundamentals-of-blender-materials-and-shading, this course will help in understanding the different shader nodes and what they do.
Keep going you will be less confused given enough time!