FTP (File Transfer Protocol) is a method for transferring files between your computer and the web server. Upload to server is usually done using a free FTP application.
We recommend CoreFTP a basic FTP program. You can download it here - https://www.coreftp.com/
To set up FTP access, create an FTP account in cPanel's "FTP Accounts" section and use an FTP client (e.g., listed above or FileZilla) to connect to your server using the provided FTP details.
You will need to key in your FTP username and password (which may be different from your cpanel password) then upload your content to public_html folder or a temp directory.
You can use SFTP (port 22) to upload as well using the same method above.

You can only use Cpanel's file manager to upload your content. In cPanel's File Manager, navigate to the appropriate directory and use the "Upload" function to select and upload your files.