If you have a widget on the same card you can just access it by name
So like if you have a field called field1 you can just use field1.text or whatever you need.
If a widget is on a different card (e.g. card1) you can access it like card1.widgets.field1.text for example.
You may want to check the Decker reference manual in the "Interfaces" section where it lists all the different properties of each widget type.
Hope this answers your question :)