I bought a car from a friend who later said he lost the title. I have a bill of sale. Is that enough? How do I get a title for the car?

Ouch! Never hand over the money until you see the title.
Go to your state's department of motor vehicles (such as where you get your driver's license or car's plates/tags) and they will be able to get you a copy of the title.
Bring as much information as you can gather such as the former owner's name, the formers owner's license plate number, and the serial number of the car (located on driver's side of windshield which can be read from the outside of the windshield looking into the car).