what is my password to open a zip in archive utility

Normally it isn't necessary to enter a password. If you're being asked for one, it's probably because whoever zipped it up created it as a password-protected zip file. If that's the case, it means the password it wants is not yours, but the one the creator gave it. You may have to go back to the website you downloaded it from and see if you missed where the password was listed.

The file you downloaded is password protected. If you don't know the password then you cannot open it. Now, if your system is asking for your admin password, then enter that password whatever it is (you set it.)