Y: place and à + thing
y stands for a place (after à, en, dans, chez …) and for à + thing, as in penser à.
Tu vas à la gare ? – Oui, j'y vais.
Are you going to the station? – Yes, I'm going there.
Elle habite en Allemagne. Elle y habite avec sa famille.
She lives in Germany. She lives there with her family.
Je pense à mes vacances. J'y pense souvent.
I think about my holidays. I often think about them.
EN: de + thing and quantities
en stands for du, de la, des + noun, for de + thing or place, and for a quantity. English often drops “some / any”; French never drops en.
Tu veux du café ? – Oui, j'en veux.
Do you want coffee? – Yes, I want some.
Je parle de mes projets. J'en parle avec toi.
I'm talking about my plans. I'm talking about them with you.
Tu viens du marché ? – Oui, j'en viens.
Are you coming from the market? – Yes, I'm coming from there.
With a quantity, en replaces only the noun. The number or quantity word (beaucoup, un peu) stays at the end of the clause.
Il a des enfants ? – Oui, il en a trois.
Does he have children? – Yes, he has three.
Elle mange beaucoup de fruits. Elle en mange beaucoup.
She eats a lot of fruit. She eats a lot of it.
Where do Y and EN go?
Like any object pronoun: before the verb they belong to. In the passé composé before the auxiliary, with verb + infinitive before the infinitive, in the negative between ne and the verb.
J'y suis allé hier.
I went there yesterday.
Je vais en prendre.
I'm going to take some.
Tu veux du café ? – Non, je n'en veux pas.
Do you want coffee? – No, I don't want any.