If your phone is asking for a password but you didn't set one up, then either someone else got a hold of it and did so, or the phone is used and the last person didn't log out properly. This is a security feature, so there is no bypassing it.
If it's the former and you don't know who put the password on it, then you'll have to factory reset the phone. This also means it'll ask you to verify your Google account email and password you used when you first set up the phone (the Google account password and the password to unlock your phone are not one in the same).
If you got this used, you'll need to go back to the previous owner and try to convince them to remove their password. They will also need to log out of their Google account, at which point it should be factory reset and have you set it up from scratch with your credentials. Make sure to back everything up first!