When you start creating an ad, under ‘What would you like to do?’ question, you will find second option, ‘Pramote Page Posts’ as you can see in the screenshot.
This option is more powerful than first option- Get More LIKEs, because here your ad will be keep changing and according to the posts you share on the page.
Under Your Ad section, you will see your posts in drop down menu and select the most appealing and most popular post by clicking the post and you will see the preview of the ad which will be shown in the right hand column of the news feed.
A checkbox appears below posts’ drop down menu, here the option is ‘Keep my ad up-to-date by automatically promoting my most recent post’. So your ad will be automatically updated if you check this box and your latest post will be shown in the ad. If you run a political or news related page, this option will be best for you, because all latest news will be shown through the ad and that will attract more and more people.
Facebook offers sponsored stories. That means when someone LIKEs your page’s post, the story will appear in the news feed of the friends of that friend. When your story is sponsored it appears in the news feed for sure. Otherwise, it may possible that due to heavy interaction in the news feed your story may not appear. Facebook automatically creates the relevant post’s sponsored story as shown in the sample in the screenshot.
This is how your story will appear in the news feed of friends who Likes your page post.
Important : Facebook has guidelines about acceptable and unacceptable images, language in the ad, your ad must be according to the policies of Facebook.