The best part of Joomla! is the ability to extend its functionality. The posibilities are limitless. You can easily find additional components/modules/plugins clicking on Extension-->Manage-->Install then search for the component that you need in the "Install from the web" section. Some are free and some are commercial.
To install the commercial plugin that you have downloaded from the developer's website, you can simply click on the "Upload package file" tab then browse to the component install package.