It would be good to know whether you have a CSR (which is a preliminary step prior to obtaining a certificate in some workflows) or whether you actually have a certificate already issued. These are very different situations to be in with very different next steps.
it looks like you already do have a certificate issued. In that case you do not need a CSR for anything. The WP Encrypt plugin has probably provided a complete alternative that obviates the need for this CSR.
The WordPress instructions are referring to editing text files on the server, which is normally done by logging in to the server over SSH, in common with other command-line system administration tasks. You would do this using an SSH client, such as the
ssh program in a terminal emulator if you’re using a Unix-like system, or typically PuTTY on Windows.
If you’ve never done command-line system administration before, you will potentially have a lot of unfamiliar tasks in order to edit the file as suggested by the plugin documentation. If this is the case, it might be a good to check in with the GoDaddy tech support ahead of time to be sure that they agree that this advice is applicable to your situation and hosting plan (so that you don’t waste time on tasks that turn out not to be achievable with your setup). You could also ask them whether they think there is a different way to configure the web server to use the certificate obtained by WP Encrypt (apart from the way that the WP Encrypt documentation has recommended).
If you decide to go ahead with editing the configuration files as suggested by the documentation, I’m sure that people on this forum will be happy to give you advice and explanations about any trouble you run into.