It is necessary to link your website with your domain name for the site to show up at that address. From your dashboard, click 'Domains' on the Cpanel page and check that the domain is listed. Once you have verified that, please go to your public_html file location and make sure the page you are trying to reach is located where it should be. For instance, if you are trying to reach yoursite.com/page.html, page.html should be located in your public_html folder.
NOTE: If you are using WordPress, please go to settings and permalinks and try changing your common setting type to see if this corrects your 404 issues.