What is CSR? (What is a Certificate Signing Request)
Do I need a CSR?
If you are renewing your certificate or if your certificate is expired, then you will need a new CSR.
What is the RSA KEY?
The RSA key is created after you submit the CSR. This is the encryption key that will be used to protect sensitive information.
When the SSL cert is enrolled, you'll receive the final CERTIFICATE, the RSA KEY, and possibly a CA BUNDLE. These will be 3 different groups of alphanumeric data sent from the certificate provider.