There was a light hanging in our living room turned on and off by a wall switch. We took the light down and there are 2 black wires. How do I hook the black, white, blue and green to the 2 black wires from the ceiling? Thank you

Are you absolutely certain that it is two blacks? I bet one was once white.

Do you own a tester?

Sounds like someone put in a switch loop but there should still be a white somewhere. If you had a light there, one of the blacks must be a neutral. Check as Stan says. If you find a hot and neutral, black and blue go to hot, white to neutral and green to ceiling box. Is this a fan/fixture rated box? Heavy fan? If so, install a fan/fixture rated box, cheap insurance.