Learn Italian: Le persone sono pronte.

The word sono is a special verb form that does double duty! It can mean "I am" (io sono) or "they are" (loro sono). Since Le persone (the people) acts as a "they" subject, here it means "are". You can always tell which meaning is correct based on the subject or the context.

"People" can include men and women. Why does it use the feminine plural article Le?

In Italian, the word persona (person) is always grammatically feminine, no matter the actual gender of the person you are talking about. When it becomes plural (persone), it stays feminine, so you must use the feminine plural article Le.

Why does the word for "ready" end in "-e" (pronte) instead of "-i" (pronti)?

Adjectives in Italian have to match the gender and number of the noun they describe. Because persone is a feminine plural noun, the adjective pronto (ready) drops its "-o" and takes the feminine plural ending "-e" to become pronte.

If I wanted to use a pronoun instead of Le persone, which one would I use?

You would use loro, which means "they". If it was already clear who you were talking about, you could replace the subject and say Loro sono pronte (They are ready), or drop the pronoun entirely and simply say Sono pronte.