I have a WordPress plugin that does exactly that if you are interested in using one that's already made versus making your own...
It's called SexyBookmarks and can be found here: http://sexybookmarks.net
If you would rather do it on your own, WordPress plugins are opensource and can be modified at will, so just reverse-engineer one to get the idea...
I'll give you some basic pointers though...
To get the URL of a WordPress post, simply use the following:
To get the title of a WordPress post, simply use this:
<?php echo get_permalink(); ?>
The site name can be echoed using:
<?php echo get_the_title(); ?>
You can get post content using:
<?php echo get_bloginfo('name'); ?>
<?php echo get_the_content(); ?>
There are a host of other predefined functions built into WordPress to make your life much easier, and finding them is as simple as searching the codex on http://wordpress.org