By default, all bases are accessible via a custom eniston.com subdomain. You may change this subdomain to anything you like (if available and not blacklisted).
You can also use your own domain. This can either be a subdomain to your existing domain (eg. help.example.com) or a separate top level domain such as example.com
In order to use your own domain, you will need to change the DNS settings with your domain provider. To keep it simple, you only need to create a new CNAME record and link it to your unique eniston.com identifier. This identifier is assigned to your account upon signup and cannot be changed. The identifier is not your public eniston.com url.
Further setup instructions are shown when you set up your custom domain. Your domain will receive a valid SSL certificate after the CNAME record points to the correct endpoint.