How do you, those who brush, do these details, like trees, cars, bridges, sky, etc.? I've tried to mimic some details, but it failed hardly. You can put here also some details to make my/whoever will watch this in future brush realistic?
PS: You can also tell me how do you do the atmosphere/fit the car in it?

Man to do things and details like us said u need to practise a lot!!

Yes, but I don't know WHAT DETAILS TO ADD/ do an atmosphere.

meh, lemme bump it.

For example, look at car photos and when you see something you like, try making something similar.

I'm sorry to disappoint, but this is like asking "how do I draw?" or "how do I paint".

There is no answer. You have to work it out for yourself by practising and experimenting.
As ollite as said, the best way to practice is to look at real photos and real cars. Look at the actual colours and the things in the reflections- really look closely, and don't just guess, then try and copy similar colours, similar shapes, in similar places

WHAT ?????@#!$@!$

at least some tips for atmosphere?

try to use reference images similar to the one u used as bg
and also for shiny edges see from where ur light is coming
lol im not promoting my merc but check it out maybe u'll get some info about that u want
i hope!!!