Norway in a Nutshell train, ferry, and bus tickets

Buy a through ticket from Oslo to Flam from vy.no. That will give you a reserved seat on the regular train from Oslo to Myrdal as well as a place (not an assigned seat, as I recall) on the Flamsbana from Myrdal down to Flam. Fares on the Oslo-Myrdal train vary; you'll probably save money if you buy early. Check policies for changes and refunds before purchasing.

I can't tell you how to get to Aurland. I think there are buses, but I don't know how frequent they are. Although there may be a taxi operating in the area, Norwegian taxis are notoriously expensive.

When you head to Bergen the next day, you'll first need to get back to Flam.

Buy the Naeroyfjord ferry (Flam to Gudvangen) ticket from NorwaysBest.com. I don't know anything about the cancellation/change policies there.

Buy the ticket Gudvangen-Voss ticket from the bus driver.

Buy the ticket for the regular train from Voss to Bergen from vy.no. I believe those trains don't have assigned seats and have fixed fares, so tickets needn't be purchased very early.

As mention, get a train ticket to Flåm. That ticket should be booked in advance. Once in Flåm it's a 10 minute bus trip to Aurland. The bus schedule and other information can be found at www.skyss.no and tickets can be bought from the driver.

A more fun way to get to Aurland can be to take one of the boats that travel on fjord to and from Flåm. Most of them stop in Aurland.