Learn Italian: Finiamo di preparare lo studio e il microfono. - We finish preparing the studio and the microphone.

Many Italian verbs require a specific preposition to connect them to another action (an infinitive verb). Finire (to finish) always takes the preposition di when it is followed by another verb. So, "to finish doing something" is always translated using finire di followed by the infinitive.

In English we say "finish preparing". Why doesn't Italian use the "-ing" equivalent (preparando) here?

When a verb directly follows a preposition like di, Italian always uses the infinitive form (the base form ending in -are, -ere, or -ire). Because of the preposition di, you must use preparare, not the gerund preparando.

Why does the sentence use lo for studio but il for microfono?

Both are masculine singular words, but they start with different sounds. You must use the definite article lo before words starting with an "s" followed by another consonant (like studio). You use il for most other consonants, like the "m" in microfono.

I remember that finire is an "-isc-" verb (like capire). Why is it finiamo and not finisciamo?