Learn Farsi: پیراهنی، کتی و شالی داخل اتاق هستند. - A shirt, a coat, and a scarf are inside the room.

You can tell by the -ی suffix attached to the end of the nouns! In Farsi, adding -ی to a noun makes it indefinite (like "a" or "an" in English). So پیراهن means "shirt", but پیراهنی means "a shirt". The same rule applies to کتی (a coat) and شالی (a scarf).

Is there an invisible sound connecting داخل (inside) and اتاق (room)?

Yes! Because داخل acts as a preposition of place here (inside of), it needs to connect to the next word with an invisible "e" sound, known as the Ezafe. You pronounce the phrase as dâkhel-e otâgh.

Why is the plural verb هستند (they are) used if clothes are inanimate objects? I thought inanimate plural subjects take a singular verb.

You are right that inanimate plural subjects usually take a singular verb in Farsi. However, when you list several distinct items connected by "and", it is also grammatically correct to use the plural verb هستند. Using the singular verb است would also be perfectly fine here.

How do lists work in Farsi? Do they use commas just like English?

Yes, listing items in Farsi works exactly like in English. You separate the items with commas and put a و (and) before the final item. Notice that the comma in Farsi looks like this: ، (pointing upwards) to distinguish it from the Persian number two!