If you have a hosting package, please see how to Set Up a Starter SSL Certificate for Hosting Packages.
SSL Certificates work by encrypting data that is transmitted between one of your site visitors and your server. This reduces the chance that others intercept sensitive data transferred between your server and your visitors, such as credit card data.
You will be taken to the 1&1 shop to purchase either the Starter SSL or Starter SSL Plus certificate. After you have completed the entire checkout process, you can return to the 1&1 Control Panel to follow the remaining steps.