In order to import an SSL certificate, you will first need to login to your cp2.cdn.net account. Instructions can be found here:
After doing this, go to SSL, then import SSL certificate.
Here you will need to add the certificate name, PEM format Certificate Key and Private Key.
After doing that, you just need to go to the resource listing in cp2.cdn.net, edit the resource, enable SSL, check custom SNI SSL, then select the Certificate name from the drop down list in order to attach the certificate to your resource.