Our XSL-FO services has two main functions.
XSL-FO Request - When you build the complete XSL-FO document in your software and just want to generate a PDF document
XSL-FO Transform Request - Here you provide XSL-FO document formatted as XSLT, and also an Xml Data Document containing the content data of your PDF and which the service will apply the transform document on.
To see full specification of XSL goto W3C (World Wide Web Consortium) website on https://www.w3.org/TR/xsl11/, and in particular chapter 6 about Formatting Objects on https://www.w3.org/TR/xsl11/#fo-section.
When generating PDF documents from data sources, XSL Transformations makes it easy to combine your data with XSL-FO documents. Get familiar with XSL Transformation on W3Schools tutorial https://www.w3schools.com/xml/xsl_intro.asp.
To get started quick and easy with your xsl templates check out PdfBroker Template Tool