I was wondering if you could explain to me what exactly the haftorah is, and how they are chosen, and by whom.

Thank you for sending this question. The haftorah was instituted during the second Commonwealth, during the times of Greek reign, a time when the Jews were forbidden from reading the Torah. Therefore, the Rabbis of those times decided to read a section from the prophets that would remind them of the weekly Torah portion. You will notice, if you read the weekly haftorah, that each week the selection that was chosen always has a similar theme to the Torah portion. Even though we read the Torah today we remember our history by living it. Therefore, we still read the haftorah even until today. I hope that this clarifies this subject for you.

Be Well,
Rabbi Litt