"Du/de la/des" vs. "de"
Okay, so I know that "de + an article" (du/de la/des) are used as partitive expressions (to express part of something). And I also know that when one wants to describe a general idea, he/she uses "de" without contracting it with an article. However, I'm still a little fuzzy on when to use which. Also, just a plain old article like "le/la" can be used to express a general idea, so what's the need for "de"? I'm just a bit confused...Could someone maybe help me, give me a few rules?
I think you omitted a very important usage of them, a usage I run into here on duolingo all the time.
They are also used to indicate the unknown quantity of something, usually food or drink.
'Je bois du lait.' - I drink (some) milk. After negative constructions (ne....pas de) and adverbs of quantity (beaucoup de) you don't use 'le/la'.
I don't really know what you're asking about, because "de" can be used for different things.
For example, it can be used for the possessive form : "Le chapeau de cet homme."
Maybe you could give examples where you're struggling to grasp the meaning of "de" ?