Yeah, I don't think you "get" pandora. The service has been around for years and arose from the old Music Genome Project that was created in order to classify every song based on 400 different "genes" or attributes. Pandora lets you create your own streaming stations based upon a song or artist and it then builds dynamic streams of songs similar in makeup to your song or artists "genome". As you thumbs up and thumbs down songs it builds a better picture of what you're wanting to listen to. So if you start thumbs-downing AC/DC songs, you won't hear AC/DC songs anymore. If you thumbs up every Metallica song it'll play more Metallica (so be careful with what you thumbs-up, remember it's not just "I like this song" but more like "play songs just like this one"). I've got 8-9 pretty well defined stations at this point that I can listen to for hours without a thumbs-down.
If you want something that gives you more freedom to listen to exactly what you want when you want it, try GrooveShark. If you want something you can click and forget more like a radio station keep with Pandora.