To use the new feature, you just go to publish an update to your Facebook Page like you always would. Once you click in the text field, the “Promote” drop-down button will appear below the field. If you click it, you’re given the option to select how much you want to spend on what is essentially an ad buy.
The number of impressions your post receives will depend on how much money you put into it, and you’ll be able to track your progress for the three days that the promotion remains in effect. That said, there is a human review process here; the Facebook team looks at the post to confirm its validity before it gets promoted.
In the meantime, though, the post appears in your fans’ News Feeds normally. Think of it like a cheaper alternative to Facebook Ads that appears only to people who’ve already engaged with your brand.