[dorota sloma] “What I don’t know is what is Redshift, when it’s needed and if I need it at the very start of learning?”
Redshift is a third-party GPU-accelerated renderer which was recently purchased by Maxon. It is one of many options available for 3D artists looking for faster rendering and more control over rendering. Since C4D has built-in rendering you do not need it, or any other third-party renderer, while you are learning C4D. Once you get proficient with C4D in general you can then decide if Redshift, another third-party renderer, or C4D’s built-in options best fit your needs and budget.
For a comparison of most of the renderers available, see the link below. Octane is another very popular renderer which isn’t included in the article.
https://www.toolfarm.com/tutorial/in_depth_3d_renderers/