if i have some index.html\index.php in any directory of my website.. is there any way that some amateur hacker can get the directory listing of that directory and directly download files from that directory
Depends on your server configuration for a variety of reasons. Don't forget that a user can always just attempt to brute-force it (a.php, aa.php, aaa.php, b.php, ab.php...)
In general - don't rely on it. Obfuscation isn't security. If someone -could- do it, assume they will. Make sure files you don't want downloading are not downloadable in the first place.