Du and le
When do I use de+article And when do I use just the article? Like 'elles boivent le lait' or 'je bois du lait?'
De means 'from' or 'of.' When it is put with an article like le, la or les, it turns into (always) du, de la, or des.
This could mean 'some of the' if you are talking about food. Je mange de la salade. I am eating SOME or SOME OF THE salad. je mange la salade = I am eating salad
Je mange la pizza. = I am eating pizza, or I am eating THE pizza
Je mange de la pizza = I am eating some pizza, or I am eating some of the pizza
I agree. Using the article by itself indicates either (1) a specific case (or serving) of something OR (2) all of the thing present (in the world, or house, or whatever "the greater context" might be). Using "de" with an article (called the "partitive") makes explicit the fact we usually assume in English that you're referring to a general quantity of something ("some"). The partitive basically means "some," but is required where we might leave out a determiner in English (e.g. "I'm eating soup." = "Je mange de la soupe.").
@savourtardis, yes de + le => du, de + la => de la, de + les => des @Spaid, I think that the partitive means "some of" but that phrase can be dropped in English. Je mange la pizza. =/= I am eating pizza. You need the "the" in there or else it means that you're eating all of the pizza in the world. If you want to say "I'm eating pizza," you need the partitive -- "Je mange de la pizza."