Every CMS has procedures for installing an add-on componenet. If installation problems arise it could be that an XML file is not provided or named properly, the zip file is too large or the zip file needs to be unzipped first before installing more zip files.
If the file is too large, it can be installed manually in some cases. For Joomla, you unzip the plugin, module, component or package of any combination and move it into a temporary directory. Then you install it from that directory.