Boosting a post is a great way to reach a larger local audience, from the main menu select "Social" -> "Page Posts", from here you can see all the post that have been recently published to your Facebook page.
Each post has an "Action" button, select "Promote" and follow the prompts.
Targeting
When setting your targeting you can use either an address with a radius or enter specific postcodes. You can enter as many postcodes as you need.
Boost Guidelines
Facebook generally recommends running a promotion for a minimum of 7 days with an average Ad spend of $5 -$10 for best results. You can run a promotion for as short a time as 2 days and Ad spends for as little as $5.