Certificate signing request help

Ok, trying to get a SSL for my blog as I plan to start selling straight from my web site. The thing can be, it requires a new certificate signing request (csr). I don’t know what a csr actually is. I have the search engines searched it to death and get found nothing practical. I am using yahoo hosting. I have also searched all over yahoo help section and can even not find nearly anything useful. I will become calling yahoo each morning but if anybody knows anything useful that would help as I’d personally really like to accomplish a lot on my site starting up tonight. Thnx for almost any help.