Learn Turkish: O öğrenci, aynı zamanda öğretmen. - He is a student, and at the same time a teacher.

In Turkish, the "to be" verb (is/am/are) isn't a separate word. For the third person (he/she/it), you can just place the subject and the noun together. So, O öğrenci simply means "He is a student," and adding öğretmen at the end means he is a teacher, too.

How does the phrase aynı zamanda work?

Aynı means "same", zaman means "time", and -da is the "at/in/on" suffix. Put together, aynı zamanda translates literally to "at the same time." In sentences like this, it acts as a conjunction meaning "also" or "as well as" to connect two facts about someone.

Could O öğrenci also mean "That student"?

Yes, out of context, O öğrenci can mean "That student." However, the pause in speech (represented by the comma) shows us that O is acting as the subject pronoun "He" (or "She"). If it meant "That student," the sentence would translate to "That student is at the same time a teacher," which is possible but less common here.

Do I need to repeat the pronoun o before öğretmen?

No, you don't need to repeat it. Just like in English where we say "He is a student and also a teacher," Turkish lets you drop the second subject because it is already obvious who you are talking about.