Learn Farsi: مامان در اتاق است.

In Farsi, the verb almost always comes at the very end of a sentence. So instead of saying "Mom is in the room" like in English, the Farsi sentence structure is "Mom in the room is", which ends with است.

Where is the word for "the" before "room"?

Farsi does not have a definite article like the English word "the". The word اتاق simply means "room". We know it means "the room" from context, because we are talking about a specific location where Mom is right now.

Is در the only way to say "in"?

در is the standard, written word for "in". However, in everyday spoken Farsi, people usually use the word تو instead. Both are completely correct, but در is what you will see in books or formal writing like this sentence.

I often hear Farsi speakers drop the word است. Can I do that here?

Yes, in casual spoken Farsi, the "is" verb است often shrinks to a simple "e" sound added to the end of the previous word. In everyday conversation, a native speaker would likely say اتاقه instead of اتاق است.