Finally – The public preview for Azure AD is now available in the new Azure portal (Azure Resource Manager) portal.azure.com

Azure AD has always only been available in the Azure classic portal (manage.windowsazure.com)

You can read up more on it here https://blogs.technet.microsoft.com/enterprisemobility/2016/09/12/the-azuread-admin-experience-in-the-new-azure-portal-is-now-in-public-preview/

You can pin the Azure AD in the portal.azure.com like this

You can then view the public preview of Azure AD