Its another word for saying oh no! when something goes wrong that is not that bad to take seriously.
you can say it anytime instead of saying Oh no!
a friend: you spelled that word wrong!
me: oh noves!!
a friend: you missed a spot!
me: oh noves!!
a discreet word for saying poo.
He just went for a poohaga!, He smells like poohaga!! , I am going for a poohaga.