Learn Italian: Ci sono cinque bicchieri vuoti. - There are five empty glasses.

No, numbers from two to ten like cinque (five) do not change to match the noun they describe. Whether you are counting masculine words like bicchieri (glasses) or feminine words, the number stays exactly the same. The only number that changes based on gender is uno (one).

Why do we use ci sono instead of just sono?

Ci sono specifically means "there are." If you just used sono, it would translate to "they are." The word ci here acts like "there," and combining it with the plural verb sono (are) is how Italians state that multiple things exist in a place.

The word for glasses is bicchieri. Does that mean the singular form is bicchiero?

Not quite! The singular form is bicchiere (glass). In Italian, nouns that end in -e in the singular always change their ending to -i in the plural, regardless of whether they are masculine or feminine.

Why does the adjective vuoti (empty) end in an -i?

In Italian, adjectives have to match the gender and number of the noun they describe. Since bicchieri is a masculine plural noun, the adjective vuoto (empty) must change its ending to the masculine plural form, which is vuoti.