There's a much easier way to do this. Download
[url=http://http://extensions.joomla.org/extensions/social-web/social-share/social-multi-share/14094?qh=YToxOntpOjA7czo5OiJpdHBzb2NpYWwiO30%3D]itpsocial[/url] (or itpshare, both free)
go into your extension manager, add it, and configure your buttons where and how you'd like. The link is to The Joomla! Extensions Directory, where you can get more info. I'm not associated in any way with the developers, but I use itpshare on my site.
If you would like to do it the hardcoding way, that can be done, instead.