How do you get from Couch to Concert Hall?
One measure at a time. It's those tiny steps, the little things like knowing each note, knowing every finger, figuring it all out, and then moving to the next measure to repeat the sequence, that will get you where you want to go.
To get you started on learning the Moonlight Sonata, Adagio Sostenuto movement, here's the first measure. Once you get this one, do the next, and the next. One at a time.
If you want all of the measures at once, and the music to go with it, click here.