The standard steps for installing a custom security certificate or SSL are to get the CSR generated [which is unnecessary for most SSL renewals, just the first installation], provide that to the certificate authority, and then get the CSR and possibly some other bundled files in return.
Once you have that bundle you can upload the files through your SSL tools in cPanel.
SSLs REQUIRE a Dedicated IP address assigned to your cPanel for the last stage -- Activation -- of your SSL to work. Additionally, you can only have one SSL per cPanel account.
Specific steps:
1. Navigate to SSL/TLS Manager in cPanel
2. Generate a Key under "Private keys (KEY)"
The Generate portion is at the base of the Private Keys screen.
3. Generate a CSR under "Certificate Signing Requests (CSR)"
4. Once that completes, download the CSR and provide it to the certificate authority [GoDaddy, Comodo, etc.]
5. Get the CRT and bundled files from the certificate authority.
Upload the files to the "Certificates (CRT)" section [you may need to UNZIP them first].
6. Navigate to "Activate SSL on Your Web Site (HTTPS)"
7. Select the exact domain name for the SSL that you had generated.
The information should automatically populate for the CRT in the upper box.
8. Most browsers require the bundled file(s) that came with your CRT.
Open the bundle or ca/chain file in Notepad and copy the contents into the CA Bundle box.
9. Once that is all uploaded click on "Install Certificate" to activate it for your account. Test https://domain to see if everything is working
If you run into any trouble getting things in place it may be easiest to assist you via phone or chat, so feel free to contact us!