1. Click on the cog-icon on the top right and go to Account settings
2. Go to the Single sign-on tab.
3. Chose Google (OAuth 2.0) as the authentication method and enter your Google domain.
4. Optionally set Allow login with username and password, if you want to allow users in iLert that are not part of your GSuite organization, and therefore, will need to login via email/username and password.
5. Optionally set Provision new users on first sso login, if you don't want to manually create users in advance and have them automatically created on their first SSO login.
No, only a single domain is supported.