First, make a order of SSL certificate.
After payment access your Client area >> Services, and click in view details of certificate SSL:
In next page, click in View certificate Details
In next page, click in configure certificate, and you will see the page below. in Web Server type, choice 'cPanel / WHM', after this access cPanel(but do not close this page), to get CSR of your domain.
You can access cPanel in http://<seu dominio>/cpanel
In Cpanel, access SSL / TLS:
After this click in generate, view, or delete SSL certificate signing requests.
You will see this screen, fill the data, and proceed.
After this your CSR,your CSR will be generated, select and put in the Client Area
After you submit your CSR and data of SSL, you will see this page:
We prefer the first(HTTP based validation), but you can choice others, to receive e-mail.
If you select first option, you see this page, just create this file in public_html of your domain, and wait to be validated.