GPAL.Form builds a GUI that belongs to your workflow - a window you design, with controls you place. GPAL.Application automates someone else's GUI - a window that already exists, with controls you locate. They share a vocabulary (buttons, inputs, checkboxes) but solve opposite problems.
A GPAL form isn't limited to one screen of static controls - FillInFrom can drive the same form through every row of a grid, file, or database query, with CallAfterFillIn running your logic between rows.
Every GPAL form control - button, checkbox, input, combo box, grid, chart, and the rest - is built the same way: a fluent chain of With... settings, completed with a cast to the control's type (e.g. (Input)) and handed to WithFormControl. Learn the pattern once and every control type follows it.
Show displays a form without pausing the workflow, ShowDialog pauses execution until the form closes, and Hide closes it - the same three verbs, but choosing between them determines whether a form is a blocking prompt or a background status window.