Carmax can buy my leased car?

Hi I am leasing a car right now, but I need to terminate this lease due to my personal reason. I called Carmax and they said that they can buy my leased vehicle. But I dont own the vehicle. How does it work? Is anybody went to Carmax and turn your car ?? She said that she will need to do the appraisal too. Uhmm, I have no clue. Please help!