Seeing and trying is believing.
To use the free version, simply go to your Administration panel, select Plugins -> Add New and search for idea exchange. While it does not have the bells and whistles that are in the Premium version, it is fully functional, a great way to learn or introduce yourself to the concept and gives you the opportunity to see how the plugin works.
Alternatively, go to https://wordpress.org/plugins/your-idea-counts/ and Download the zip file. Then, in your WP Admin dashboard, go to Plugins -> Add New to upload it to your site followed by activating it.