Conversion tracking can help your business measure the return on investment of Facebook Ads by reporting on the actions people take after your ads are viewed.
For example, if you want to track checkouts, you would put the conversion tracking pixel on the checkout confirmation page that people see after completing a checkout. Whenever a person loads that page, the code tells Facebook that the conversion event has occurred. Facebook then matches that conversion event against the set of people who viewed an ad or clicked on an ad so that we can provide you with information that helps you understand the return on investment for the amount you spent.
Conversion tracking also helps you show ads to people who are more likely to convert off Facebook. Learn more about optimizing for conversions.