Hey Brian,
There are many tutorials out there on the web as to how you can use OpenSSL to create a CSR.
Here's a document produced by OpenSSL.org which is very good. You can also read about it on many sites by googling.
Generally, this forum is meant for broad discussion of the platform and its services, not for 1-on-1 technical support or questions. This question might be better answered by consulting Google or maybe posting a question to stackoverflow or serverfault, although I'm sure there are already so many questions and answers on this same topic that to create a new one would invite "duplicate" flags.
Overall, there's a wealth of information out there that I encourage you to access, and I wish you the best of luck in getting your certificate set up. As you go, make sure to consult the docs on
Custom Domains and SSL.
Best wishes,
Nick