Not sure how it works at all... and do you have to buy the token on the same server you play?

You buy gold from someone on whatever server they are selling it. You make a level one and run to main city, trade gold, go to ah buy a token, redeem it for either game time or blizzard balance. Sometimes you can get lucky and someone is selling the gold from your server but not always.
If you are selling tokens reverse this process.

Also you can just buy time which is a service I offer through just time codes which has no token involved and just grants you a month of play time. PM me if you want