au and avec
Could someone explain when to use au and avec?
Ohhhh! Yeah you're right. It's just sort of an expression in french to say "au lait" instead of "avec lait".
If you're saying "Voulez-vous du café au lait?" ("Do you want coffee with milk?") then here "au" would mean "with".
It is very confusing and even with French being my second language I don't fully understand. I think it might be like coffee with the flavour of milk. Like for example "Gateaux au chocolat." (Chocolate cake.") It's the same sort of concept.
https://hinative.com/en-US/questions/20722 This link might also help answer your question.
In this case, when you are refering to a flavour of something, you use à + l'/le/la rather than avec:
un café au lait - a milk coffee (i.e. a coffee with milk)
un gâteau au chocolat - a chocolate cake
un sandwich au fromage - a cheese sandwich
une glace à la fraise - a strawberry ice-cream
une tarte à l'orange - an orange tart
Edit: I want to add another example just because in the above the gender of the flavouring just happens to match the noun, so I want to add another one where it doesn't:
une glace au citron - a lemon ice-cream
Depending on whether the setence is in the past, present, or future "au" can either mean "to" or "at". If the sentence is in the present, "au" means "at" and if the sentence is in the future or in the past, "au" means "to".
So for example if you're saying "Nous allons au magasin." (We're going to the store.") or "Nous sommes allés au magasin." ("We went to the store.") in these two sentences "au" would mean "to". But if you were saying "Je suis au magasin." (I'm at the store.") then "au" would mean "at".
But you shouldn't always use "au" for "to". If you're saying "Je vais à l'épicerie." (I'm going to the grocery store.") here you would use "à" instead of "au" because "l'épicerie" is feminine. So use "à" before a feminine word "au" before a masculine word.
"avec" simply means "with"
So if you're saying "Je veux un hamburger avec du fromage." (I want a hamburger with cheese.") here "avec" would mean "with".
My first try to assist my fellow learner - au is short form for "a + le" which is "to the / at the" in English, au applies to masculine only; example, to(at) the park = au parc". For feminine example, "to the house = a la maison", do not use "au" here. Avec simply means "with", for example, "with my brother = avec mon frere", or, "with my mother = avec ma mere".
The most confusing is that in the Duolingo lesson they had the phrase " Du cafe au du lait", which means some coffee with some milk flavor. However, the phrase in English that was given to translate into French is " Some coffee with milk". Why can't you write " Du coffee au lait"?