Learn Farsi: آن خانم معلم است.

In Farsi, the verb almost always comes at the end of the sentence. While English puts the verb in the middle ("That lady is a teacher"), Farsi puts it at the end, so it literally reads "That lady teacher is."

Where is the word for "a" in "a teacher"?

Farsi usually drops the word for "a" or "an" when stating someone's profession. Instead of saying "a teacher," you just use the noun معلم (teacher) on its own.

Why do we use آن here instead of او (she)?

آن means "that". Because it comes right before خانم (lady), it acts as a pointing word to mean "That lady." If you just wanted to say "She is a teacher," you would drop the word "lady" and use the pronoun او (she/he).

Does خانم mean "lady" or "Mrs."?

It can mean both! On its own, like in this sentence, it means "lady" or "woman". However, when placed after a name, it acts as a respectful title, like "Mrs." or "Ms."