In the four-level hierarchy that characterizes a MoStack the fields and controls are the fourth and most detailed level: A card has a number of fields and/or controls on it, defined in the background to which the card belongs, and the fields hold the values.
Regarding the number of parameters that are possible to configure fields and controls, they are the most complex level.
Among the many parameters, the one defining the type of a field or control is the most important one. MoStacks supports text, integer, float, date, time, boolean, list, command and picture fields/controls. You find details about the supported types in the chapter Field and Control Types.
There are a number of flags that influence the display and the behaviour of the fields and controls, as a way to refine further beyond the types. You find them detailed in chapter Field and Control Flags.
Fields can be "empty" or "undefined". Read more about this special state in the chapter Undefined.
The formatting of values for some types is country-dependent. You find the details about this in the chapter Internationalization.
By the way, there is sort of a terminology problem here. Technically fields and controls, however called, are one and the same. They are just the "things" that make up background definitions, and the "things" that cards have to hold values and enable interaction.
Now, on the one hand programmers are used to call these things controls, but this seemed to be a term that is just a little too technical for the target audience of MoStacks to be used exclusively. On the other hand, an attempt to use field for everything leads to Command field, which is a little strange.
So, as a compromise, both terms are used.