In order to buy and install a digital certificate, you must first generate and submit a CSR (Certificate Signing Request) to a Certification Authority or a reseller of a Certification Authority.
The CSR is generated by your web server software, which will also create your public/private key pair used for encrypting and decrypting secure transactions.
Click here for CSR-generation instructions for all supported server software.
Please note that if you are applying for a certificate on a shared hosting account then you'll need to
contact your provider to generate the CSR on your behalf.