Affiliate since: 03/15/2013, Power Rank: 99999999 | Read John's 50 other Ask SC answers

T-Credits are like Currency at TripleClicks.

They can be used for Bidding on Auctions and purchasing items at TripleClicks or
You can list your stuff for sale on your T-Connect page with them.

You can purchase them or win them in the hourly drawing.

This is the simple explanation if you just want to help someone understand easily.