This page gives you a basic idea of how FlowForms works. The FlowForms plug-in can render the corresponding elements based on a certain schema. You can use the 'Load Samples' button to load different examples. You will see the schema change, and the FlowForms plug-in will rerender the form.

You can add JSON schemas you find on the FormKit website; make sure you first validate that it is valid JSON as the schema on the FormKit website is not formatted correctly.
You can use the following formatter: JSON Formatter