Ne is a partitive (pronoun). This means it is used to express a portion “a part” of a quantity. It can mean several things in English, usually on the order of “some of it/them,” or “about it/them,” or “of it/them.”
1. As a pronoun, it can replace nouns that express an unspecified quantity.
Ecco delle fragole buonissime, ne vuoi?
Here are some great strawberries, do you want some of them?
Quante sorelle hai? > Ne ho due.
How many sisters do you have ? > I have two (of them).
Quanti libri hai portato? > Ne ho portati molti.
How many books did you bring? > I brought a lot (of them).
2. Ne can also replace phrases introduced by the preposition di when the significance of di is closest to the English “about it,” or “about them.”
Parlate degli amici che avevate in comune? > Sì, ne parliamo molto.
Do you talk about the friends you had in common ? > Yes, we talk about them a lot.
Hai paura dei fantasmi in questa casa? > No, non ne più ho paura.
Are you afraid of ghosts in this house? > No, I’m not afraid of them anymore.
Hai voglia di un gelato? > Sì, ne ho voglia, grazie.
Do you feel like having an ice cream? > Yes, I’d like one, thanks.
3. Position of ne. Similar to the rule for direct- and indirect-object pronouns, ne usually precedes a conjugated verb but it can be attached to the end of an infinitive after eliminating the final –e of the infinitive.
Vuoi mangiare della pasta? > Sì, ne voglio mangiare molta! OR Sì, voglio mangiarne molta!
Do you want some pasta? > Yes, I want a lot (of it).
4. Agreement with ne. Past participles will agree with ne in the same way that direct object pronouns will. (See Section 10.2 above.)
Hai tagliato tutte le rose? > No, ne ho tagliate solo la metà.
Did you cut all the roses? > No, I only cut half of them.
5. There is a popular idiomatic expression using ne to express the date:
Quanti ne abbiamo oggi? > Ne abbiamo sette.
What’s today’s date? > It’s the seventh.