The station is very clean and organised , with the office for Supratours based next to the entrance. If you want to travel comfortably and not too expensive ,the Supratours busses are the best solution. You have to book in advance ,at least 24 hours I guess. There are a couple of busses going per day ,all with air con ,for about 70 Dirhams. The actual bus station is further down the street next to hotel Ibis. If you have luggage you have to book it in for some Dirhams before you get on the bus.
We did Marrakech - Essaouira and return ,but they do a couple of other destinations too.