Once you've generated an SSL key and CSR, you can purchase a signed SSL certificate from a Certificate Authority (CA).
One option for an inexpensive SSL certificate is the PositiveSSL certificate from Namecheap. ServerPilot does not have any affiliation with Namecheap, PositiveSSL, or Comodo. We only mention this option because it is inexpensive, and we believe they will issue certificates that work when your domain is accessed both with and without www.
When buying your certificate, select Nginx as the server type. If Nginx is not available as an option from your CA, then select either Apache or Apache+OpenSSL.
Once you receive your certificate, go to the SSL tab in your app's details page in ServerPilot. Enter the SSL certificate you were sent, and ServerPilot will configure the SSL certificate on your server.