Login by clicking the My Account link top right of that page.
Watch the video here for details.
Using Your Sygnal Domains Account
Once you are logged in, here are some tips to get around;
At the top, see the “Domains” tab. Click that to manage your domains, add new ones, etc.
Click the very top Sygnal Domains logo or the "My Account" text in order to return to the home page of your account at any time.
If you want to add a credit card for automatic renewals, you can do that from your account home page, or by clicking this link.
Here's a screenshot of the Domain Name screen which appears.