In very simple PHP applications, many people will choose to execute their code in the order the results appear on the screen. On the other hand Joomla runs each module and components separately, then assembles everything into the template.
Joomla is designed in such a way that you never have to touch the core files. Aiding in this, Joomla provides five different types of extensions giving you a wide range of control over how Joomla loads and executes. It's possible to write all five types of extensions for both the site and administrator applications of Joomla
While most people know Joomla as a content management system, Joomla is also a platform where any number of applications can sit on top. Let's take a look at three that are prepackaged with the CMS. So first go to the root of a fresh copy of a Joomla installation and open up index.php.
What if you don't have hosting account
You can use various offline software packages which can emulate exactly like a hosting environment (webserver).
These tools are free to use. They are good for testing and learning and you don't require an internet connection to test your joomla website! But it has some major drawbacks too. One major drawback is that other people can't see your website! for this you have to buy a hosting space so that whole world can see your joomla websites.
In order to install joomla 2.5+ you need the following requirements in your hosting environment:
To find more detailed installation you can check on the following links: