You can download it from there and load it into your plugins directory on your server. Then you need to run the install for it and activate the plugin. At that time you will run their setup program and decide which of the social network links you want on your post.
I use all of them but you may only want to run specific ones. There are check boxes for the ones you want.
What
Sociable then does is place links to all the chosen social networks so that your users can repost your blog posting to their own social networks. Of course this ends up in getting you links. The full list of networks is below:
What I am suggesting for all my customers and also doing for myself is registering at all these social network sites. Then as you post articles you can click on each link and post that article to your account at that social network. You will be amazed at how much traffic this will get you. Here is the complete list. Please contact me if you would like more information.