la particella ne

Ne is used as a pronoun to replace di + noun or di + infinitive. Its rough meaning is of or about it, them, him, her, etc., though often in English we leave these terms out.

Examples:

Parli di tua sorella? - Certo, ne parlo spesso. (= Certo, parlo spesso di mia sorella.)
Do you talk about your sister? - Of course I talk about her often.

Hai paura dei topi? - Ma no, non ne ho paura. (= Non ho paura dei topi.)
Are you afraid of mice? - No, I'm not afraid of them.

Hai bisogno di riposarti? - No, non ne ho bisogno. (= Non ho bisogno di riposarmi.)
Are you in need of rest? - No I'm not in need of it.

You also use ne to replace nouns that come after a number or an expression of quantity like molto, quanto, troppo, un po’ di, un chilo di and so on.

Examples:

Quanta birra bevi? - Ne bevo molta. (= Bevo molta birra.)
How much beer do you drink? - "I drink a lot of it."

Quanti figli ha? - Ne ha tre. (= Ha tre figli.)
How many kids does he have? - "He has three of them."

In the examples above, we would probably omit the “of it” and “of them” in English, but ne in Italian is mandatory in this context.

Like any pronoun, ne goes before the conjugated verb, bumping non back in negations, or attaches to the end of infinitives.

Non ne parlo perchè non voglio parlarne. (or non ne voglio parlare)
I don’t talk about it because I don’t want to talk about it.

When ne is used in the past to replace a noun used with an expression of quantity, the past participle agrees in gender and number with the noun ne is replacing.

Quante birre hai bevuto? - Ne ho bevute tre. (“Bevute” is feminine plural to agree with “birre”.)
How many beers did you drink? - I drank three of them.

You also use ne to express the date:

Quanti ne abbiamo oggi? - Ne abbiamo otto.
What’s today’s date? - It’s the eighth.

Another place where you’ll commonly find “ne” is in the special verb “andarsene” (to go away).

Andarsene is made up of the verb “andare” (to go) + the reflexive pronoun “si” + “ne”. As you may know, when combining direct and indirect object pronouns, mi, ti, ci and vi become me, te, ce, ve when followed by lo, la, li or le - e.g. Me lo dai. Similarly the reflexive pronoun becomes me, te, se, ce, ve or se when followed by ne. It’s important to point out that andarsene is purely idiomatic. The si is not reflexive in this case, and the ne is not playing any of its usual roles (described above). They are just for emphasis. As a substitute for andarsene, you can always use “andare via.” Now let’s see it in action.

io me ne vado, me ne sono andato/a, me ne andavo, me ne voglio andare, etc. 
tu te ne vai, te ne sei andato/a, te ne andavi, te ne vuoi andare...
lei se ne va, se n’è andato/a, se ne andava, se ne vuole andare...
noi ce ne andiamo, ce ne siamo andati/e, ce ne andavamo, ce ne vogliamo andare...
voi ve ne andate, ve ne siete andati/e, ve ne andavate, ve ne volete andare...
loro se ne vanno, se ne sono andati/e, se ne andavano, se ne vogliono andare...

And the imperative:

Vattene! (Go away!)
Se ne vada!
Andiamocene!
Andatevene!

A verb similar to andarsene is fregarsene (used mainly in the negative to mean “not to care about something,” a bit rude). Other verbs that always go with pronouns (though not ne) include…

cavarsela - to get by. Parli l’italiano? – Me la cavo. (I get by.)

farcela - to succeed at something. When Italy won the World Cup '06, a lot of fans exclaimed, “Ce l’abbiamo fatto!” You also often hear it in the negative as a term of exasperation: “Non ce la faccio più!” (I can’t take it anymore!)

averci - to have. All over Italy, in speech especially, not in writing, Italians use “averci” as a variant of “avere.” “C’ho fame. C’ho un motorino. Che c’hai?”