The Best way to explain Tripleclicks and TCredits to someone that has never heard of them is this:
Tripleclicks is like a Sears or Walmart a store online that you can purchase your everyday items and special items.
If you have ever been on EBAY...you know you can bid on items to buy in a certain time period.
TCredits are like those bids but they can be any value. They are like a token representing the value you bid. When you have 100 TCredits you are able to bid that many times.