Install rtSocial plugin from the 'Plugins' section in your dashboard (Plugins > Add New > Search for rtSocial).
Alternatively you can download latest version of rtSocial plugin from the repository. Unzip it and upload it to the plugins folder of your WordPress installation (wp-content/plugins/ directory of your WordPress installation).
Activate it through the 'Plugins' section.
Adjust the plugin settings from the settings section (Settings > rtSocial Options).