You need to read the manual to see what that USB port can use. It is very very odd that the car has a USB port but no aux in or bluetooth. I have never seen a car with a USB port without an aux jack or bluetooth in the radio. The USB things in the post above won't work, one is some odd cable used for charging or syncing, not for audio play back, other is a computer audio card that needs drivers installed to use.
You may need to check the radio to see if there is an option for an aux in to be wired into the rear of it.
Otherwise you will need to do a lot of fiddling with things like using a bluetooth to FM adapter then getting an aux to bluetooth transmitter. May be better to just spend $100 and get a newer radio. I got my wife one from BestBuy for $120 including installation but without adapter costs.
My F150 and my wife's Navigator have USB only (NO 3.5mm or other ports) and you can charge or connect external audio; but we also have bluetooth. Depending on the year your car was produced, it may be a charging port only.