The first step in using Facebook ads is to go to http://www.facebook.com/advertising/ while logged into your personal account. If you are currently using your Page, Facebook will instruct you to switch over to your profile. After you reach the page listed above click on the green box "Create an Advert" in the upper right corner.
That will being up the page above. Here is where is gets tricky. Some people think you should aim people to your shop URL and I disagree. I think you should point the Ad to your Facebook Page. That way you can advertise to those who like your page over and over again. Pointing them to your shop is a one time deal. Having them as a fan means they have to go out of their way to "UnLike" you.
You are able to also promote a specific post or story on your Facebook Page. Here again I think just getting people to "Like" your page should be the goal. The more Fans you have, the better chance you have at having some of those fans buy from your shop.
Tomorrow I will go through some of the things that you need to do with your ad and some of the things you don't need to do. Let me know if you have any questions!