"He looks very calm on stage."
Translation:Sahnede çok sakin duruyor.
Yes, the verb "durmak" means "to stop" indeed. Or "to stand" for "(ayakta / hazır) durmak". But in Turkish sometimes the verb "durmak" is used with some adjectives and so gives us different meanings.
He looks angry. = (O) Kızgın duruyor / görünüyor. (He has an angry face and we can see this.)
She looks confused / bewildered. = (O) şaşkın duruyor. (He has a confused look and we can understand this.)
The child looks sad. = Çocuk üzgün duruyor / görünüyor.
The man's jacket looks very bad. = Adamın ceketi kötü duruyor / görünüyor. (The man has a bad jacket or the jacket doesn't fit / suit to the man.)
That is; if we talk about sensitive adjectives or a thing whether suits to someone we can say "adjective + durmak" for "looks angry / bad / calm".
But we don't use "adjective + durmak" for every situation all the time.
So; for this situation (for your example) "O yorgun duruyor" is not usually common in Turkey. But you can say "O yorgun duruyor." Because it isn't a wrong use grammatically. Only we don't use like this. Instead of, we say "O yorgun görünüyor."
That is not absolutely clear to me. "Yorgun" isn't a sensitive adjective? I can see if anybody is tired, for example rings under his eyes etc. Is duramak only used with angry/bad/calm? And can't I use görünmek with calm and confused? What about bakmak? When will I use this verb? Can't it be used here because it is needing an object?