I downloaded facebook app on my android device. After downloading, there's a prompt saying that it can't be installed and there appeared an error , Error code - 24.
Welcome to Android Central! Which device is it? The model number you gave seems incomplete.
If Sam_Gs7 is correct and the Facebook app was preinstalled, then when you search for it in the Play Store, it should only give you options to Uninstall, Open, or Update (if there's an update).