SSL certificates are issued by Let's Encrypt.
Certificates will be added to your domain automatically, this may take a couple hours.
To get your certificate instantly login to your cPanel account and view the SSL/TLS Status page and click the Auto SSL button.
Your domains name servers need to be updated to your plans proper name servers for your SSL certificate to be applied.
If your certificate fails to be applied the most likely cause is your domain is not resolving to the correct IP yet, this can take up to 72 hours.
SSL certificates are applied to all domains added to your hosting account.