Upon arriving on the facebook Debugger page, you will see something like this:
What you see is in the image is an input box of the URL of the blog page, post, etc. that you would like to preview. You have to make sure that the link that you are trying to debug is scrapable by Facebook or else you will not see any result because it will appear as Facebook URLs aren't scrapable by this Debugger. Try your own.
The result of your activity will give you an idea of how the social networking site understands of looks at your link and understand what is inside the link. There will be warnings that will help your verify if the result of the open graph is correct or not.
You will then be provided with the things that should be fixed. A better understanding of the usage of Facebook Debugger Tool will help you become more accustomed with share preview. This is simply a preview of what to expect once your link is already placed or shared in Facebook. If you can predict what would be the outcome of your link and be sure that things are fixed and no errors are detected by Facebook with your link, then, there will be order on your posts and efficient sharing of your pages, etc.