The number of extensions for Joomla is fast approaching two thousand, just counting those listed at extensions.joomla.org. Every day, new extensions, and updated extensions are posted at that site. Some are excellent, but some are not ready for general use. The best way to determine what is useable is to read the ratings and reviews, and the Editors' List. Keep in mind, though, that an expert may be able to use an extension that is too advanced for the beginner to intermediate user. There are often simpler extensions that give most or all of the functionality of the more advanced extension.
    There are three kinds of extensions: Components, Modules and Mambots. With the release of Joomla 1.5, Mambots have been renamed Add-ons. The extensions are usually compressed, and the name usually begins with the kind of extension, such as com_jce.tgz. They are installed by going to the installer, choosing Component, browsing to find the compressed file, and uploading. The user will then see a notice that the installation is a "Success."