"He is our cook. I live in a mansion. I have these things because my aunt is rich." "thats what all rich people say!"
if I say "lui è nostro cuoco", is it considered wrong? do I always need the article?
You need the article in this case. You do not need the article for something personal, like my hand or my brother, but you do need it for the plural forms of family members.
Well it has been a while since I did those lessons... Maybe hand wasn't a good example, but I do vaguely remember that "my pocket" might not an article, is that correct?
I think it's possible to say "la mia tasca." I don't know the lessons you're referring to. I know there's something funny about body parts where you use the indirect object for the owner, like "Mi sono fatto male al naso," "I've hurt my nose."
So not using articles is actually an exception? As a rule the article is almost always needed?