"This is very difficult."
Translation:Bu çok zor.
bu is nominative and buna is dative. "this" is the subject here and it can only be "bu".
if it were "I am looking at this" - "to look" uses a dative object in Turkish- it would be "Ben buna bakıyorum"
buna is an indirect object, bunu is a direct object and bu is nominative so can be the subject
Can i know what is The in turkish like for examle :yeşlı adam, in translation they bring the old man but how can i know the sentence should be having the in turkish
There is no word "the" in Turkish. It must be derived from context normally (English requires "the" in many places where you would see nothing in Turkish)
Do bu/şu/o depend only on physical distance? Why did i ask - because in Russian we can say something like this: "do you see THAT woman? - THIS is my mom". Something, which we talk about, becomes "close"
Yep! It is similar to the English "this" and "that." There is a third option for something far away but not super far away (and that is old information) "şu"