Son doesn’t know how to feed himself

You can try giving him big pieces of fruit or baby cracker or teether. It's easier to hold biggee stuff with his whole hand. It might take a while and he might be just playing and throwing the food around, that's OK let him freely explore, play and improve his motor skills. When he's good at it already you can slowly try smaller food like blueberries to practice pincer grasp (picking things up with only thumb and index finger).