The home page in a default installation replicates the public Liferay website. There is a link in the upper right corner that takes the user to the login page. If it is not available in your installation you can go directly to the login page by using this URL: http://your-host-name.com/c/portal/login.
Once you are in the login page you will be asked for the following information:
The default installation is configured to login by email address. It comes with a preconfigured administrator account whose address is [email protected]. If you are not using the default installation you should ask the administrator which authentication system the portal using (login name or email address) and the information of an account that you can use.
The password of the preconfigured administrator account is test.