If you have just had an account set up on your Looker, you will receive a setup email with a link to finish setting up your account. When you click this link, it may take you to a login page (rather than a page prompting you to finish setting up your account). This is happening because LDAP or SAML is enabled on your Looker instance. These services allow users to log in using a common username and password across multiple sites.
If you know what your common username/password are, log in with those credentials!
If you are unsure what those credentials are, talk to an administrator for your Looker. They will be able to point you in the right direction.