Welcome to Android Central! Has this always been your phone? If you did an unauthorized factory reset (i.e., resetting without first removing the Google account that's associated with the phone), then that triggers Factory Reset Protection, which is meant to discourage thieves from stealing a phone and simply doing a factory reset to make it their own. It's asking for the Google account and password that was originally associated with the phone. If this is your phone with your Google account associated with it, then try to recover your Google account here:
Google Account Recovery. If this hasn't always been your phone, then you'd need to contact the previous owner and ask them to help you log into the phone.
