Hi,
Here's what worked for my 4 year old...
I didn't actively train her until she hit 3...when she started to show interest in about 2 1/2 years old...he may still be a bit young, but you can start getting him interested but don't put any pressure on him...
We did the following:
-Elmo Potty DVD - it's AWESOME and the kids really get it...
-read books about potty training too...lots of them out there...
-when YOU or someone else goes to the bathroom, have him go with you and talk about it - show him pee pee in the potty and poo poo too...
-take him to the store and let him pick out his underwear! :) Make a HUGE deal about it - "see you have underpants like Daddy now!" To prevent accidents, I put the pullup OVER the underpants...that way, when he goes, he feels REALLY wet but not cause you to change his pants all the time...
-one thing I tried (but didn't work for us) was have him go outside with a long tshirt on with nothing on his bare bottom...when he has to go - he'll notice that there's no diaper on his butt and may try to tell you that he needs to potty. OR if you notice him peeing/pooping, GRAB him and put him on the potty (I used the potty and placed it outside on the deck). But be prepared to watch him ALL day. My daughter hated this, held it in until naptime/bedtime when I had put a pull up on her and she went all at once in the pullup! Ugh...
-some people do M&M's for rewards, but I didn't want to associate FOOD for rewards...so the FIRST FEW times my daughter went pee/poo in the potty, she got to watch whatever movie she wanted...after that, I tried to cut down and give her other sorts of rewards...even at 4 years old, she tells me that she went poo-poo in the potty all by herself and I make a big deal and give her a HUGE hug! :) She doesn't have accidents either, which is great! :)
-nighttime - if you notice that he pees overnight, he may not be ready and you'll still want to use diapers for overnights...until you notice he holds it...and reduce fluids before bedtime...
It may be frustrating BUT he will get it...eventually...no rush and definitely don't put any pressure on him...