The manage domains page of the panel must show "fully hosted" following that a "user" is listed.
Log into that specific user. There you will find a directory named the same as your domain name. This directory was automatically added for you when you added hosting for the domain under this user. Uploading here will be visible via the web server.
1) You switch to the directory named for your domain and upload index.html. Navigating in a browser to your domain, the index.html will be displayed.
2) In the same directory named for your domain name upload a picture, if that picture is named example.jpg then your browser will be able to find the picture at example.com/example.jpg