I have a 2 1/2 year old son. My husband and I got him a potty chair at about 15-18 months of age and put it in the bathroom. Whenever either of us would go in to use the bathroom, he would go with us and we would just sit him there to get used to it.
He started showing signs of wanting to potty train around 18 months (early for a boy all of our friends said). It was hit and miss, but we would praise anything he did (lots of clapping and smiles - no rewards yet).
We kept at this til he was 2 1/2 (this past Feb) and literally one day he got up went poop and pee in the "big boy toilet, like daddy" and from that day forward we got him "big boy" underwear. We had a few accidents at home and at daycare, but within a month (by the time he actually was 2 1/2) he was completely potty trained; at school, at night and on trips to the store or anywhere else.
On the other hand my nephew who is 3 has just started pooping in the toilet.
Not every situation is the same, but you can always introduce the potty chair to him and let him take the lead from there. Patience is the key... there were plenty of frustrating times I went through since my husband wasn't home all the time to help me out with our son. Good luck!!!!