What is default or home page filename?

Your default filename is index.html or index.htm page. So you can reach your site instead of typing the whole www.yourname.com/index.html, you can just type www.yourname.com on your browser.
However, if you developed sites using PHP or Perl you can use index.php or index.php3, index.cgi are also supported.
Please make sure you DO NOT upload your hompage, index.html or index.htm in uppercase for example like Index.html or Index.htm or INDEX.HTML. Please make sure your homepage index file is in lowercase.