#1
In terms of I-II-III-IV-V-VI-VII what do each of the realtionships do? Do they create a mood or something?
Ibanez RG350DX
Line 6 Spider III
Cubase SX3
#2
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.
#3
Quote by greeny23
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.
#4
is there any websites that can tell you the different relationships?
Ibanez RG350DX
Line 6 Spider III
Cubase SX3
#5
end your piece of viidim (i don't know how to make the little circle that indicate dim chords)