'Wo ist der Bahnhof, bitte?' means 'Where is the train station, please?'. 'Gehen Sie links und dann rechts' (go left and then right) gives directions. 'Nehmen Sie U3' means 'take U3' but doesn't say where the station is. 'Nach Marienstraße' alone isn't a complete direction. 'Guten Tag' is just a greeting.