Iterators let you loop through iterable collections in your input data. Each iter items can then be referenced in 'Data Fetcheres' by the alias you specify. Each Item in the data collection will result in a new object of the object the iterable is added too
Attributes
Attributes are the key value pairs in json that actually holds data. For example if the object is 'car', an attributes can be number_of_wheels with value 4. Start by giving the attribute a name.
Objects
Objects are key value pairs like Attributes, however the values are Attributes instead of strings or numbers. The objects are for example 1 'invoice' that holds attributes like 'amount', 'address' etc.