WHAT IS A CSR?
CSR means “Certificate Signing Request”. It is a block of encrypted code containing information regarding you and/or your business, as well as your public key. CSRs are encoded for practical reasons, but you can easily decrypt any CSR and see the information contained. Here is a tool to do this.
Certification Authorities will use your CSR to issue your certificate: they use the information you added on the CSR to create the certificate. This is why it is very important that your CSR has the right information and the right public key.
There are various ways to create your CSR from your server. However, keep in mind that when you create a CSR, you also generate a private key at the same time, which will be encrypted and stocked on your server. So each time you create a CSR, you create a new private key.
Each CSR is then unique, and only works for the private key generated with it. As SSL certificates are also generated from the CSRs, they will also only work with the specific private key generated with the CSR.
This is why your SSL certificate won’t work anymore if you format/change your server, or if you lose the private key.