The CSR is a string of text generated by your server software. You provide this string of text to Certificate Authority (CA) during the enrollment process to enable SSL Certificate to issue an SSL Certificate unique to your Web server. You will need to know what kind of server software is running on your Web server to generate a CSR.
The Secure Sockets Layer (SSL) is a security protocol used by Web browsers and Web servers to help users protect their data during transfer. An SSL Certificate contains a public and private key pair as well as verified identification information. When a browser (or client) points to a secured domain, the server shares the public key with the client to establish an encryption method and a unique session key.