what does it mean for hard sleeper and soft sleeper

They are two berth types and the comfort degree and ticket price is different from each other. The hard sleeper cabin is open and equipped with six bunks, respectively upper, middle and lower berths on each side, while there are only four sleepers in the soft sleeper cabin. For more detailed info, you could visit the page: https://www.travelchinaguide.com/china-trains/tickets.htm