to build on Pauline's answer, other than hiking up the steep path up the cliff edge, the two ways to Muerren both involve a large cablecar. These cablecars are quite large. I've never counted but I would guess that they hold 50 to 75 people standing. They are quite quick.
The simplest way to Muerren is from Lauterbrunnen, directly across the street is the cablecar up to Grutschalp where the passengers change onto the train along the top of the cliff to Muerren. They had to put in a cable car to replace the previous funicular which suffered from ground movement.
If you can't put up with cablecars that's fine, but it is a very scenic ride.
Wengen is on the opposite side of the valley, the side which is much lower and much flatter. Also car-free, it is reached by train from Lauterbrunnen. From Wengen the train goes up to Jungfraujoch via various intermediate villages and junctions. Wengen is also linked to the ridges via cablecars.
Grindelwald is yet further over, reached by trains from Interlaken, and linked to the trails by cablecars and the train up to Jungfraujoch via a different route for some distance. It also has plenty of cars and buses.