Hello! I want to ask about that strange black reflections on the bottom of the glasses. When i try to render my own glass the bottom looks very flat and unrealistic, like between of the glass layers was nothing. I mean this part on the real photo below
How can I get this effect? Thank you in advance for any tips
The reflection and refraction are driven primarily by the illumination plus background/surrounding environment.
In this image you have a bright (possibly back-lit) background and floor, darkness to the sides plus maybe a dark background to the front and top - and you have illumination from the front.
Look up some tutorials on glass rendering and see if you can replicate their lighting and background setups.