From Interlaken Ost station, there is an hourly train to Lauterbrunnen (make sure that you board the correct section of the train in Interlaken, as the train divides at Zweilutschinen). Once in Lauterbrunnen, follow the directions on the signs. You will make the ascent to Grutschalp in a cable car. From Grustchalp, a train takes you along the ridge to Mürren. On a clear day, the view from the train is spectacular. Be sure to sit on the left side of the train for a view of the valley below.
Mürren is a beautiful car-free village. Everything is accessible on foot.