Action Details
Requirements and how-to articles for Facebook's action:

You need this to get it done:

Photo Post
A photo post which you want to be boosted.
Decide whether your goal with this boosted post is to receive more post engagements or more messages.
Post Button (Optional)
Decide whether you want to add a call-to-action button to your post (e.g. Sign Up, Shop Now, Learn More, etc.)
Target Audience
Decide on the audience you want your post to reach (gender, age, location, interests, etc.)
Duration and Budget
Choose how long you want your post to be boosted and what your budget is.
Choose currency, enter payment details and pay.
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

Facebook Ads Help Centre - The difference between boosted posts and Facebook ads
How boosted posts work, and how they differ from regular Facebook ads.
Link missing here or found errors? Improve How-Tos