Very easy to install, similar to rest of the plugins.
- Download and unzip the plugin simplest_facebook_twitter_googleplusone_sharing.zip.
- Copy the unzipped folder in your Plugins directory under wordpress installation. (wp-content/plugins)
- Activate the plugin through the plugin window in the admin panel.
- Configure the settings through Settings->Simplest Fb Twitter Google+1 Share in the admin panel.