In terms of I-II-III-IV-V-VI-VII what do each of the realtionships do? Do they create a mood or something?
they can indeed create mood, they can also add tension, or create an ending. for example chord V-I is a "perfect cadence" or the best way to end a peice.
V-I is a "perfect cadence" or the best way to end a peice.
It's debatable whether it's the best way to end a piece, but it's certainly one of the most common.
is there any websites that can tell you the different relationships?
end your piece of viidim (i don't know how to make the little circle that indicate dim chords)
well yeh, personally i usually prefer IV-V or IV-I but thats just me...
http://www.musictheory.halifax.ns.ca/22cadences.html <--- there maybe?