How do I get my 6 month old Neapolitan mastiff to sit and come when i call him?

Hold a treat in your hand and make a hand single so that he will know when you want him to sit. keep add it with him for a few weeks or so then lose the treat. put him on a long leash then go as far as the least can go then show him the treat and tell him to come here that will take a few weeks or months.