Explanation
Box 1: Hides the control in the body of the form.
The Client API form context (formContext) provides a reference to the form or to an item on the form, such as, a quick view control or a row in an editable grid, against which the current code is executed.
setVisible sets a value that indicates whether the control is visible.
Box 2: Add an event handler to enable a function named TestFunction to run when the business process flow stage changes.
addOnStageChange adds a function as an event handler for the OnStageChange event so that it will be called when the business process flow stage changes.
Reference:
https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/clientapi/clientapi-form-context
https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/clientapi/reference/formcontext-data-p
https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/clientapi/reference/formcontext-data-p