Every social network has a url which allows you to easily share your site. Facebook’s sharer.php and Twitter’s ?status= are the most common examples. Google plus has one as well:
// Set up the window attrubutes
var attributes = "toolbar=0,location=0,height=450,width=550";
// Format the share url
var url = "https://plus.google.com/share?url="+escape(pUrl);
// Open the window
The Google+ share uses facebook’s open graph meta-tags to derive the title, description, and image. Add these to the page you’re sharing to further customize the post. You can view the button in its own page to see the source, as well as some extra code to center the window on screen.