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

paid action
Create a slideshow ad to appear in users' News Feeds.

You need this to get it done:

A short description to accompany your slideshow (maximum of 90 characters.)
Choose up to ten images to use in your slideshow.
File format: .jpeg/.jpg or png
Resolution: Minimum of 1,280 x 720 pixels
Ratio: 16:9/1:1/2:3 (should be consistent across all images, otherwise slideshow is automatically cropped to 1:1)
Video Stills
Choose a video to use stills from.
File format: .mov/.mp4
Either upload your own audio (if you own the rights to it) or choose from the list of available music tracks.
File format: .wav/.mp3/.m4a/.flac/.ogg
Add captions to your slideshow (a large amount of Facebook users have video audio muted whilst browsing their News Feed, so captions are very useful for helping to get your message across without relying on audio.)
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 ad to run and what your daily 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 - Create a slideshow ad
Step-by-step guide on how to create a slideshow ad.
Facebook Ads Help Centre - Tips for slideshow
Useful tips for creating effective slideshow ads.
Facebook Slideshow Ads
Information about slideshow ads - when and how to use them.
Link missing here or found errors? Improve How-Tos