You can find the terminal number on your e-mail confirmation when you first book a flight. The gate number is typically offered when you check in for your flight online or in person at the airport. You can also find your gate number on the monitors at the airport that show information about departure and arrival times.
Make sure that you are present at the gate at the boarding time indicated. Passengers who report to the gate too late are not allowed onto the flight and lose their right to transport. Gate changes also happen, and you should be alert to this possibility as well. When checking in, many airlines now offer a text notification service for these types of changes or provide this information through their app. Take advantage of these options if possible to stay as informed as you can.