If you are tracking conversions, you can segment your website visitors into groups based on the actions they have taken on your website. These groups are called custom audiences. Once you have defined a custom audience, you can optimize your ad sets to target other Facebook users who match that audience's criteria.
Before you can define a custom audience, make sure the Events Manager is tracking your events or custom conversions correctly, otherwise you will not be able to select them in the Events Manager when setting up a custom audience.
To define a custom audience from a standard or custom event, follow the instructions in our About Custom Audiences from your website Business Manager help document.
To create an audience from a custom conversion, follow the instructions in our About Custom Audiences from your website Business Manager help document, but select People who visited specific webpages at step #4. Use the same URL criteria that you used to define your custom conversion.