Help. My dog is a patterdale terrior and tends to snap/nip people. how can...

♥ Becky ♥

...i train him? he is 8 months old and can be a pain when people walk past the house he barks and growls if someone walks down the street, is there a way to train him to stop it?also when people put there hands by his mouth/nose (so he can get there cent) he hates it and snaps he is known to bite but he does give a warning out (he growls) i want to train him because he is v.good with us (his owners, he's also good with some of my sisters friends) he tends to growl/bark/ if someone knocks on the door however if they just walk in without knocking then he seems absolutly fine. i know that the breed are teritorial animals - what does this mean, is this bad or good could i have some training websites/trickshe is toilet trained - can sit- can lay down and is mastering play dead. he is an average learner (fast learner if food is in the trick ) please help mei'm 14 and i got him for my 13th birthday in august - hes already a dear member of the family and my uncle has recently took care of one of the puppies from the same litter/pack and his mum and dad come to visit him (his owner brings them up or we bumb into them in the park) and s family friend brought a puppy from the same litter/pack. there is no way i'm giving up on him now and i need your help (he has been known to nip/bite some people - they stuck there hands by his mouth - )