Hi poisson.
You first need to configure your social network settings. To do this, head to the Settings option in your WordPress admin dashboard and click the option named Social Feeder.
Here you will see different configuration tabs, the first one is called general, with the general settings. And the other ones are one per each Social Network supported by the plugin. Head to the tab of the desired social network and follow the instructions displayed in the contents of the tab to set it up.
Once configured, head to the widgets section of your admin dashboard and drag-and-drop social feeder widget to the sidebar of your desire. The feed should display in the sidebar of your choice.