It can be used in various contexts like:
* "Kakoye u tebya nastroeniya?" (Какое у тебя настроение?) - "What is your mood?"
* "U menya horoshee nastroeniye." (У меня хорошее настроение.) - "I am in a good mood."
* "On byl v plohom nastroeniyi." (Он был в плохом настроении.) - "He was in a bad mood."
So, essentially, "nastroeniya" refers to the emotional state or disposition of a person at a particular moment.