An extension whether it be a component, module, plug-in or template is installed by clicking the 'install/uninstall' link in the 'Extensions' menu in your Joomla control panel.

As you will see there are three different methods for installing extensions however the 'Upload Package File' method is the easiest. All you need to do is click the browse button locate the extension on your computer and click install. DO NOT unzip the extension first, Joomla will unzip the file for you and then copy the contents to the necessary locations on your site.

Unfortunately the 'Upload Package File' method doesn't seem to work well on some Joomla sites hosted with H4P therefore you need to use the 'Install from URL' method. To do this you will need to upload the extensions zip file to your site then insert the URL to the zip file. For example if the extension is called extension.zip and you upload it to the root directory of your site then enter http://www.yoursite.com/extension.zip into the 'Install from URL' field.

You will either get a message saying the installation was successful or an error message. Possible reasons for an error message could be that you need to unzip the extension first. Sometimes an extension is comprised of multiple files such as a plugin.zip and a component.zip which are zipped up into one single zip file. Therefore you first need to unzip the file first and install the individual extension zip files one at a time, make sense?

Another possible reason for an error is because you may be trying to install a component which is compatible with Joomla 1.0 only and not Joomla 1.5. Most extensions should tell you on the download page which version they are for.