One time pinatawag ako sa school ng anak ko kasi may problema daw . When i got there the principal explains to me that my son bullied one of his classmate i was shocked coz i dont even realized that he can do that . Whats the best thing to do to explain to him that what his doing is not right ? Do i need to punish him for doing that ?

Punishment is different from disciplining. I guess what you have to do is to discipline the child. He has to know the pros and cons if he continues to become a bully. Give him scenarios that would make him realize how is it to be bullied and what is the feeling of a bullied person. As a parent, be there to guide him until such time that he understands and commits that he won't do it again.