Well i follow
-> https://en.9jcg.com/comm_pages/blog_content-art-10.htm
this tut but really i don't get all the point of how HDRI work and what exactly it is .. can someone explain in a few words but to be understandable ... i see that my ball reflected the image but as u see in my Render image i don't get the effect which the man in tut get ... and im asking my self why ... i follow every step of the tutorial and i can't find what mistake i made .. maybe it's the point of not mentioning about how must i set my Mental reay settings ?