When you registered in the Elements Catalyst app, you created a username and password.
When you get to the login screen provide your email address that you used during registration and click next:
You will be taken to the next screen where you will be asked to provide your password. If you have forgotten it, simply click "Forgotten your password".
However, if you are a member of a corporate domain controlled by your organisation with enabled SSO you will be taken to your corporate identity provider. If you were provisioned to Elements from Salesforce or if you set up your login preference to be Salesforce then you will be taken to the Salesforce login screen.