Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. crt.sh | example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.
Without the answers to a lot more of those questions, and specifics about what you're trying to do, it's going to be very hard for anyone here to help you. Generally you don't "download" a certificate from anywhere, but you have software that manages requesting, managing, and installing it wherever your system needs it.
Maybe the first question is, are you using some kind of "shared hosting" where your only access is through some control panel, or are you administrating web servers yourself?
There shouldn't be any manual steps in certificate installation. If your cPanel doesn't have the automatic system enabled to just get and use certificates for you (which is really what should be the case), but the cPanel is set up to allow for the use of other certificates, and if your hosting can run PHP scripts, then you might want to use CertSage. It's a PHP script that can request the certificate and automatically install it into cPanel.