Good question 🙂 This is a very important structure in French. In your example: "There are some books." → Il y a des livres. "Let’s buy one." → Achetons-en un. What does ''en'' mean? ''En'' replaces something introduced by: - de (des, du, de la) - a quantity Here, ''des livres'' becomes ''en''. So: - Il y a des livres. - Achetons un livre → Achetons-en un. 👉 En = “of them” / “some of it” It avoids repeating the noun. More examples: - Tu veux du café ? → Oui, j’en veux. (I want some.) - Il a des frères ? → Oui, il en a deux. (He has two of them.) - Tu as acheté des pommes ? → Oui, j’en ai acheté. So whenever you refer back to something introduced by de / des / du / de la, you can often replace it with en. You’re asking exactly the right A2 question 👍