The Flow scripting engine is object oriented. Everything with the script is an object, and each object is of a certain class. The class determines that the object can do.
For instance, the Data Set class provides access to the records and fields of the data. From there you can access a Field class which provides access to the actual value of the a field.
Other classes provide access to the properties of the modules configured within Flow. For instance you can access the File Connection or DB Connection modules from within the map.