ha, I told you I don't know how it works! ...I made up "related", as in music similar to music to music you own. don't know of that feature in spotify.
Oops, my bad. Not even sure there is a related feature

Anyway, here's how it works. Once you download the client app, you open it, and search for what you want to listen to (album, artist, song, what have you). Then you listen. Repeat.
Really is worth getting it (for free)... has me really psyched on new stuff.