Posting organically (for free) on Facebook is not enough to guarantee people see your content.
When you post to your business' page's news feed you usually have the option of 'boosting' it which means paying money to increase the number of people who see it. Boosting a post is the simplest way to advertise on Facebook. Under each of your posts you will see the option to Boost.
When you choose an organic post to boost you are able to do the following:
Choose your objective: do you want to get more people to react, comment and share your post or do you want to send people to your website?
Choose who you want to reach: you'll pick a target audience of the type of people you want to connect with. If you're trying to reach a local audience, then simply enter your location or region
Say how much you're willing to spend: you'll state how much you want to spend over the course of your entire campaign.
Choose how long you want to run your ad: once you click Boost and your ad is approved, people in your target audience will see your ad in their News Feed for the duration you've set.
If you don't want to boost a post from your organic news feed and don't want your ad to be seen organically - you can master a new post and instead of clicking Publish, click Boost.