How to install a Magento Extension
Many of the Magento beginners are not aware of the fact about the extensions available in magento to add extra modules/functionality to their shopping portal. You can find all the available magento extensions here http://www.magentocommerce.com/magento-connect/
What you need to do is search the extension of your requirement and register your account in the website. If it is a free extension you can find INSTALL NOW button by selecting the Platform (Community/Enterprise) and also the Magento connect Version ( Magento Connect 2.0 is what we prefers). Then agree to the license and click on get extension key.
Copy the key from the magento connect page. Login to your Magento Admin Panel, Navigate to System -> Magento Connect -> Magento Connect Manager where you need to login again with your Magento Login Credentials.
You will find “Paste Extension Key to Install”, Paste the key which you copied from Magento Connect and click on Install. Follow the instructions on the screen and finally at the bottom click on the refresh button if your extension installed correctly as per the comments on the black background screen. Return to your admin panel to find your newly installed extension configuration settings.
Don’t forget to log out once from your admin panel and login again to see your extension configuration page from admin since most of the extensions shows a 404 page immediately after installation.
Now you can install any extension the same way through Magento Connect !