A grueling experience is one that leaves a person physically or mentally exhausted. You could also say that the person is very tired from working, but the word "grueling" is much better at describing the level of stress that is felt. The word "grueling" is an adjective that is almost always used to describe a thing (an experience) but not a person.
The students had a grueling final week of school before exams.
The teacher gave a grueling test.
Rhonda had a grueling day at work.
After a long, grueling day at the office, Pete was exhausted. (He was very tired.)
Working at a pizza place on a busy Friday or Saturday night is absolutely grueling, but the wait staff makes a lot of money in tips.
Rowing the boat from one side of the lake to the other was a grueling experience.