Learn Farsi: سگ سیاه ما را می‌ترساند.

ما means "we" or "us". Because "us" is the direct object here (the ones receiving the action of being scared), we must add the direct object marker را. Together, ما را is the Farsi way of forming the independent object pronoun "us".

How do you pronounce the connection between سگ (dog) and سیاه (black)?

You need to add a short "e" sound between them, pronouncing it as sag-e siyâh. This hidden linking vowel is called the ezafe. It connects a noun to its adjective, which in Farsi almost always comes after the noun.

Does the verb می‌ترساند mean "scares" or "is scared"?

It specifically means "scares" or "frightens" (causes fear). The dog is doing the scaring. If you wanted to say the dog itself is afraid, you would use a slightly different verb form: می‌ترسد (is afraid / fears).

Will Iranians actually say ما را in a casual spoken conversation?

Usually, no! In everyday spoken Farsi, را is shortened to رو (ro) when it follows a vowel. So, in real life, you will almost always hear people say ما رو (mâ ro) instead of the formal written ما را.