Learn Italian: La carne è ottima, ne mangio un pezzo. - The meat is excellent, I am eating a piece of it.

In this sentence, ne means "of it" (referring to the meat). When you mention a quantity like un pezzo (a piece), Italian uses ne to show what that quantity is of, saving you from repeating di carne (of meat).

Why does ne go before the verb?

Just like the direct and indirect object pronouns you have already seen (like mi, ti, and lo), the pronoun ne is placed directly in front of the conjugated verb. That is why we say ne mangio and not mangio ne.

Why is the word for excellent ottima ending in -a?

It ends in -a because it describes la carne (the meat), which is a feminine singular noun in Italian. Ottima is the feminine singular form of ottimo, which means excellent or extremely good.

Since la carne is feminine, why doesn't un pezzo change to match its gender?

Because un pezzo (a piece) is a completely separate noun, not an adjective describing the meat. Nouns have their own fixed gender. Pezzo is always masculine, no matter what it is a piece of!