It is important to understand that a child usually does not have sphincter control until age 3. That doesn't mean that some children aren't able to be trained before 3. However, the physical control doesn't happen until 3. Some children are more obedient and will try to do what you tell them. I would not use punishment at his age since, as I said, he has no sphincter control yet. There are Books for Potty Training. You may want to try these.
"Potty Time With Abby":http://www.amazon.com/Potty-Cadabby-Editors-Publications-International/dp/141277781X
"Potty Time With Elmo": http://www.amazon.com/Potty-Time-Elmo-Liittle-Sound/dp/141273486X