you must upload everything in your public_html directory (that's how it called on hostgator but, on other hosts/systems can be called htdocs, www or something else )
delete everyting from inside the public_html directory
create a file named index.html and put this into it
HTML:
<html><body>Hello</body></html>
save it and upload it to the public_html directory
This is just a test, navigate to your domain:
If nothing shows up call hostgator and ask them to help you, otherwise if your browser says 'Hello' go back to the public_html directory, delete that file and upload your website ( prosper, simple files, wordpress, anything...)
only what's inside public_html can be accessed via http, all the rest is there but can't be reached using a web browser.
PS: you could have figured this out in 1 minute checking hostgator knowledge base, requesting support via chat or simply searching google.
Good luck