Well, it depends on how old he is. In most cases, boys start later to learn to potty than girls, and take longer to accomplish the task. Generally, children cannot genuinely learn to use the toilet before the age of about 3. True independence in toileting may take boys until 3.5 to 4 years old for both urine and feces.
Teaching him how to urinate will happen first, in most cases. It is helpful if he can watch an older boy or man urinate (standing up). You can use a child size potty so that he can do this easily. Then, every few hours, lead him to the potty, have him drop his trousers and diaper (or pull up) and try to uriiate. I do not suggest things like food rewards or toys as rewards, only a high degree of praise and celebration (smiles, clapping, 'high five') and congratulations that he is becoming a 'big boy'.
Once he starts to urinate in the potty on a regular basis, begin to do the same thing for bowel movements.