This plugin automatically shares posts to facebook and twitter with predefined messages and grabs the facebook comments.
To install this plugin in your working wordpress installation just download all files and put them in a new folder e.g.: /wp-content/plugins/wp-autosharepost/
Just follow these steps to get things working for each of these social networks
In order to support URL shortening for your twitter links you should enable bit.ly by supporting the plugin with some valid login details.