What happens to US dollars sent to Afghanistan?

I've heard that a BILLION dollars has been spent there. A BILLION dollars!! And the place is STILL a mess! What in the heck happened to all those dollar bills? Was it given off as bribes? Payment for the army? Gee, my hometown coulda used some of those dollars--we desperatly need to repave some roads but don't have the money. Why? Because it was drawn off by the state....to fund...Afghanistan....