Learn Italian: Se la vite è piccola, usa il cacciavite piccolo. - If the screw is small, use the small screwdriver.

Vite is a feminine noun. Cacciavite is a compound word combining the verb caccia (from cacciare, meaning to drive or push) and the noun vite. In Italian, compound words formed with a verb and a noun are almost always masculine, regardless of the gender of the noun inside them!

Is usa the command form here? Doesn't the tu form usually end in -i?

Yes, usa is the informal command (imperative) for "use!". While the regular present tense for "you use" is tu usi, affirmative commands for -are verbs (like usare) take an -a ending instead.

This lesson is about attaching pronouns to commands. How would I change this sentence to say "use it" instead of "use the small screwdriver"?

You would use the direct object pronoun lo because cacciavite is masculine. With informal affirmative commands, pronouns attach directly to the end of the verb. So, usa (use) + lo (it) becomes usalo. The sentence would become: Se la vite è piccola, usalo.

How would I make cacciavite plural if I needed multiple screwdrivers?