which is station to get in and to get off from Milky Way hotel to west bus station in Changsha

Since your hotel is close to the CS Railway Station, so there is an easy method for you.
You can walk to the Railway Station where you can find the local subway line 2 and take it to reach its terminal at Wangchengpo Station. Get out of the station from Exit 5 and walk along Yulan Road to Fenglin 3rd Road, on which the West Bus Station can be easily found.