Trains normally depart from the Hlavní nádraží main station while buses leave from either the main Florenc station or the southern Roztyly station, accessible from a metro stop on the Red (C) Line. When exploring your transport options, look into the Student Agency. (It’s just a name; services are for everyone.) They offer more direct routes, plus free hot drinks and videos on board. Tickets must be purchased ahead of time; they have a window at the Florenc station.