How do the painter and the author create those moods

When all these elements are balanced, Nihal can be reasonably sure of creating the effect she's after ... Every painting strives to generate some sort of mood; value in the composition plays a powerful role in evoking stuff

They express their moods on the their works or outputs from where? what? or maybe whom?

they might be influenced or just they feel it because thats the way they wanted to feel.