CPanel is a part of the web server which would allow you to make changes in the code for the website. It can be also used to perform administrative action as well.
SSH is a command line Linux tool which one could use to perform actions on the server. It is particularly useful if you want to Install some package or library in the server. One just has to type in a couple of commands and it gets Installed.
Since one could make a lot of changes on the server using SSH, this access is not given to everyone who has a login to the webserver. The only person who has access is the site administrator. In order to use SSH for your web server you need to Install a client. Putty is one such client which could be Installed. One has to put in the user name and password and then you log in. But sometimes it is not straightforward as it seems to be. Many times you won’t get access right away even if you are the administrator. There could be Issues regarding IP address, since some servers by default blacklist all IP addresses for security purposes. In that case one has to whitelist the IP address manually.