Generate CSR and install SSL certificate from within cPanel.

[a24uall]

Login to cPanel and click on SSL/TLS Manager
Now you need to generate a "Private Key"

Under "Private Key" click on

Generate, view, upload, or delete your private keys.

Scroll down to the bottom and there you see "Generate a New Key"
from the dropdown select the domain name.
NOTE : If you want http://www.domain.com for the SSL, simply edit the first box named "hosts" and add http://www.domain.com there.

Most probably the key size is 2048, but depends on the company who gives the certificate.
Now click "Generate" to generate the certificate.

Now under

Certificate Signing Requests (CSR)

Click on "Generate, view, or delete SSL certificate signing requests."
You can see the domain name under drop down box.
Fill the required details and generate the CSR.