hello everyone .. i am pretty new to php programming and web development and i need to ask this. i have designed a few websites for my clients and i am getting better and now i have started learning php to add dynamic feel to the websites. my question is whenever i create links in my pages i do something like <a href="index.php">HOME</a>, <a href="aboutUs.php">ABOUT US</a> and so on. So i uploaded the website and whenever i view the source code the links appear exactly like that yet in other professional websites i have seen i always see something like <a href="http://www.facebook.com/home.php">HOME</a> for example.
what am i doing wrong. how can i make better links to other pages. what is the use of building links in that format. thank you.