Like all puffers, porcs are best in a species-only tank, and like all other puffers, they are molluscavores and, therefore, eat invertibrates such as shrimp, crabs, snails, etc. They do are carnivores, so they need meat such as shell-on shrimp, clams, crabs, mussels, etc. They won't eat veggies much, if at all. They are very specialized fish and require special care. They absolutely require hard-shelled food items or their teeth will overgrown and will require dentistry or will be unable to eat and will die.
I hate to say it but I would recommend you return him to the store. They require a minimum of 100 gallons when alone, and a whole lot bigger when kept with other fish.