If you cannot read and understand this without writing a lot of uninteresting stuff about manual, your background etc. then I think you have a problem:
"I am a completely beginner and is planning to buy a D750 or D850.
But my - a little naive - question is whether D850 takes better pictures than D750.
Of course, the pictures can be printed much better, but in "normal" sizes are there difference between them?"
I am very well able to google manuals, technical differences etc. but you seem not to be able to read.