To create a new Plugin configuration just navigate to Components -> CComment -> Settings and click on new. Follow the steps on the screen and when ready click save.
To edit a plugin configuration navigate to Components -> CComment -> Settings and in the list click on the plugin config that you wish to edit.
When you install CompojoomComment for first time, configuration for com_content is automatically created. In addition to this a content plugin is installed and enabled ( extensions -> Plugin manager). Because of this once you open an article in frontend you should immediately see the comment form.