what is the difference of luxury sleeper and first class train seat

The luxury sleeper coach as a several compartments in coach. Each compartment is a room with a door and has four beds, two upper and two lower. It is recommended for long-distance trip.
The first class seat is the seat in the high-speed trains, and it is suitable for short-distance trip.
you can find more information at:
https://www.travelchinaguide.com/china-trains/tickets.htm