.htaccess file and URL rewrite rule in php

Redirect URLs using .htaccess  :   
You can use .htaccess to redirect users to a different URL(redirect a url)    
Sometimes you need to redirect some URL and/or page on your site to another one.    
using the “Redirect” directive:    
Redirect /folder http://www.example.com/newfolder      
Another useful directive is the RedirectMatch    
RedirectMatch "\.html$" http://www.example.com/index.php      
This will redirect all requests to files that end with .html to the index.php file.      
One of the more powerful tricks of the .htaccess hacker is the ability to rewrite URLs    
simple rewriting        
all requests to whatever.htm will be sent to whatever.php:    
Options +FollowSymlinks      
RewriteEngine on      
RewriteRule ^(.*)\.htm$ $1.php [NC]      
RewriteRule ^menu.html menu.php