After installation, Sociable plugin will appear in the side bar on your dashboard. Click on it.

You will be able to see this page when you can choose between Classic Sociable (landscape) and Skyscraper Sociable. Pick the one you like the best!

Might want to give some thoughts on where you want to those icons to be placed. As for me, I want the icons to appear at the end of each post so I chose Classic as having the icons in landscape is a better choice.