With a difficult customer, I would try to calm them down by just being very calm, very level-headed, very polite, and if it's still not enough, I would eventually transfer them over to a manager or supervisor to handle. Same with a difficult situation, I would try my best to figure it out and get it done without inconveniencing someone, but if it's to a point where I don't understand what I'm doing or I can't get it done myself, I would go to a manager or supervisor as the next step and learn how to do it so the next time I don't have to bother them.