Am I really playing against other players or against the computer?

That depends entirely on which game you play. Usually, online Bingo is a real-time game where you therefore play live against other players in the casino. If you are playing against a computer in Single Player Bingo, for example, this is always clearly indicated. With Live Bingo, you always play against real players anyway where you can even see the dealer at work through the camera and follow the other players live.