Learn Italian: Usi i browser più veloci, per favore. - Use the fastest browsers, please.

In Italian, nouns that end in a consonant are usually foreign loanwords, and they are invariable. This means their spelling doesn't change in the plural. We only know it means "browsers" here because it is paired with the plural article i and the plural adjective veloci.

If this is a command, why is the verb usi instead of usa?

This sentence uses the formal imperative, which is a command given to someone you would politely address as Lei. For -are verbs like usare, the informal command is usa, but the formal command takes an -i ending, becoming usi.

How does i browser più veloci translate to "the fastest browsers"?

Italian expresses "the fastest" by using the definite article + noun + più + adjective. The plural article i at the beginning of the phrase acts as "the" for the whole idea. Literally, the phrase translates to "the browsers more fast".

Why does the adjective veloci end in -i?