Copy and paste one of the code blocks into the html file you are editing... place it wherever you want the facebook link or button to be on your site.
Then in the code you just pasted, find the word "url" and type in the web address you want to be shared. Facebook doesn't determine it automatically, and here's why:
For example, you might have this button in your sidebar on every page on your site... mysite.com, mysite.com/services, mysite.com/links, etc. When folks click the link or button, do you want them to be sharing just mysite.com from every page? Or the specific page within your site that they're currently on?
So you might put http://www.mysite.com
where url used to be for each page, or you might put http://www.mysite.com/services
on the services page, for example.
Does this make more sense?