how can i get from dulles airport to bethesda maryland?

Its not difficult, just time consuming. You take the Washington Flyer Coach from Dulles AIrport to connect you to the metro (I think it takes you to the Falls Church station). The Metro is pretty easy to figure out and will eventually connect you right to the Bethesda station which is on the red line. The coach bus leaves every 1/2 hour from the airport. If you go to the website for Dulles airport (just google) you can get more specific info about where exactly to get the coach service.

If your time is more valuable to you a cab is quicker. Dulles only allows Washington Flyer-certified taxis, which I’ve found pretty reliable, and a lot less complicated than the switch from the bus to the Metro, then having to make a transfer from the Orange Line to the Red Line—all the more complicated if you have a lot of luggage. Another, cheaper option is one of the door-to-door shuttle services.

Agree with carlos; a shuttle service will be much cheaper and less confusing that the flyer/metro option. The metro is safe and easy to navigate if you go that route…remembering that you’ll also be carrying your luggage on stairs, escalators, etc.
There are shuttles right outside the trasportation door.