Generating CSR AND public key for Letsencrypt

The first part, generating a CSR is easy. I can go to DCM and generate a CSR but the website that allows you to manually create a Letsencrypt SSL cert asks for a Public Key AND the CSR. So, where would I find/generate/export a public for the CSR? To get an idea of what I am dealing with, look here: https://gethttpsforfree.com/

The recommendation there is generate the key with openssl, which I have done in the past when I have generated a non-DCM CSR. But, when DCM is creating the CSR, where do I find the public private keys? I expect that they are stored somewhere, just like when I create certs/csr's using openssl. Just need to know the location.

Or, maybe this just isn't possible with DCM...?