Here's a breakdown:
* Il: He/She/It (the subject)
* en: of it (referring to something previously mentioned or understood)
* a: has (verb "avoir" in the third person singular)
* plus: more
The phrase is commonly used to indicate that there is a larger quantity of something available.
Here are some examples:
* "Il y a du chocolat dans le frigo. Il en a plus !" (There's chocolate in the fridge. There's more of it!)
* "Tu veux du pain ? Il en a plus dans le placard." (Do you want some bread? There's more of it in the cupboard.)
* "Elle a beaucoup de livres. Il en a plus dans sa bibliothèque." (She has a lot of books. She has more of them in her library.)