No worries dude.
There's a diagram somewhere that Bill posted which explained offset well but essentially that's about right.
The amount of spacing really depends on what car it is, s3 or otherwise, and personal taste.
As an example though s3 owners tend to use 10mm spacers on the front and 15mm on the back but that's with the wider arches. I'm not too sure what is good on the a3 but I imagine doing the same wouldn't be too far off, hopefully some one will be along to confirm lol.
How wide are the wheels?