Shibboleth is what is called a "single sign-on" service. Like Athens, once you've logged in to one service, you can get to other services without needing to re-login. If you've already logged into your institution, and your institution is an active customer, you should get right into Credo. Shibboleth login is available only for members of institutions who have set up this method of login.
If you have not yet logged in to your home institution, or if you select 'Log in via your institution' from the Credo login page you will get sent to what is called our "Discovery Service". This is a page that lists all the Federations that we do business with and all the institutions in each federation.
Using the discovery service, you find your home institution either by selecting it from the long list or searching for it by name. If your institution is not listed, then this style of login will not be available for you.
Once you select your home institution, you are taken to a login page at that institution and they will ask you log in. What the login page looks like and what information you have to provide to log in depends of course on the institution. If you succeed, the institution will send you back to Credo with your bona fide credentials accessible to Credo.
At this point all Credo needs to do is determine if your home institution is an active Credo customer. If you are, you should see the Credo start page. If not, you will see the Credo login page with a message indicating that your institution was not known to us.
Your institution may link to Credo using a WAYF-less (Where Are Your From) access URL. In this case, you wouldn't have to use our Discovery Service. Avoiding the Discovery Service is not always possible though, particularly from links to entries that appear in citations or which are saved in emails.