Pages are organised as a collection of sections that are rendered on the page, one below the other. Sections have different styles wich define the apperance of the sections. Depending on the style of a section, the section has different fields which define the content of the section. The value of a field can be a simple plaintext or a collection of child sections which have their own styles and children.
For a more in-depth description of each style refer to the documentation of the source code.