For buying SSl, You have to search for CSR(Certificate Signing Request)at the place where you purchased the certificate.
After you enter the CSR, the company where you purchased your certificate will usually require you prove your identity. In most cases they will require you to either call them or fax them with the information they require. Simply follow their instructions.
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You can simply contact your Hosting service to provide SSL they will do it. For SSL dedicated IP is necessary you also have to buy it for running SSL.
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most hosting providers offer this product for resonable price. It's advised to contact hosting support about the detailed steps to issue a certificate with them, they will handle all the rest stuff after payment done.