Where is American airlines?

It can be either, check your flight here: https://www.airport-orlando.com/mco-airlines/american-airlines

Terminals A and B house American. You will need to consult your boarding pass.

Both terminals A and B.

Terminal A and Terminal B if you need to check in luggage. The gate number should be listed on your ticket. Then follow the sign to your gate for boarding.

It can be in Terminal A or Terminal B