Most new web hosting plans have a placeholder page or folder to show the website is working. You'll need to remove any pages before a new default file will show on your website. To do this, simply enter your cPanel and click "File Manager". Then navigate to the /public_html folder where you'll see an index.php or index. (something) file. Click that file and choose the delete option.
If you add a script like WordPress with our app installer it will ask you to remove the index page. Just click yes and it will do it for you.
If you want to add files, it's the same as removing them. You log into "cPanel". Then search for the File Manager:
Then navigate into the "public_html" folder. There you can upload your main index file and any other files you want to have shown on your website.
