Does he pick it up at all?
If he doesn't, the first thing to teach him is the 'get it' command. You need to teach him to pick something up with his mouth.
Go to a nice quiet room, sit down with a big bag of VERY tiny treats and a ball or stick. Make sure he is on a leash. Sit down in front of him and present the ball/stick. hold it right in front of his nose. if he touches it with his nose, praise him and reward him.. do this several times. Once he has the touching of the ball/stick down as a good thing encourage him to open his mouth and put it in his mouth. As soon as it's in his mouth say 'Good get it!' praise treat and reward. Again repeat this a few times until he is reaching for it himself..
Do this for a few days..
Once he has this down solid you can get him to hold the ball in his mouth and GENTLY keep his mouth on the object by holding his snout. Count to 3 (not out loud!), release his snout and say 'Drop it' at the same time. Once he drops it, praise treat. etc.. repeat this.. Over time, after you release teh snout he should not drop the ball until you tell him to with the 'Drop it' command.
Next, take the training to a short hallway. Sit at one end and have Mr. Dog on his leash still. Toss the stick just a couple feet away and tell him 'Get it'. He should go to the stick and pick it up. Then tell him to come to you, he should continue holding it because you haven't given him the 'Drop it' command yet. tell him to drop it, praise treat reward like he just won an oscar!
Slowly increase the distance and you'll having him fetching, retreiving in no time
This was how I taught Deja to fetch by the way.. She loved it. She got more treas than you can imagine and she loves to play fetch now. You can start leaving out the treats once he realizes it's a game.. the game becomes the reward.