If you are looking to track conversions via Wix Stores or other Wix Apps then the conversion data is automatically sent over to your Pixel, provided you have setup Facebook Pixel on your Wix Site settings.
Else you need to read the Conversion API documentation https://developers.facebook.com/docs/marketing-api/conversions-api/
If you need to make sure it is using it then install the Facebook Pixel Helper Chrome Extension (that’s if you’re using Chrome)