How to search within a defined radius using MySql and PHP

Hey guys, today my manager assigned me a task to search property listing withing a specific radius like within 10 km or 10 miles. I did it very easily because I have done this already in one of my project. But first time this task was very hard to do and I did a lot of research and goggled the internet to find out the solution. Well that is an old and long story. Today after doing my task I thought why not I post my work in the form of an article on my blog. So here is the article...