CPanel is basically the control center of your website. You can install Wordpress, monitor traffic, create databases, etc. You need to open 'Web-Based File Manager' and upload your banner image file. Next, open HTML files and link your banned image file, where you want your banner displayed.
go to file manager or just find any menu to upload file, and choose where are you want place your banner will be, ok
You can upload your file in both methods ie via FTP - you can get filezilla its a free ftp client. or you can use cPanel file manager to upload your file. Embedding the banner on your site depends on the kind of script or site you are using. If its an html page you can edit your html file and add code (check google for html codes). If its wordpress or forums it depends on the skin/theme options.