In PPL you work with an HWND (int) handle. Every control and windows have their own unique handle. When PPL (Visual Form Builder) creates it's windows or controls it uses the same handle.
The handle variable name is always the same as the name you give your control in the visual form builder + an $ at the end. Ex: If you have a label named MyLabel in the Visual Form Builder you will set it's caption with the following line of code:
SetWindowText(MyLabel$, "Text");
or
SetWindowText(MyLabel$, Variable$);
SetWindowText works for a lot of controls and the window's title bar as well.
Check
http://www.msdn.com for technical reference. PPL uses pretty much the same functions for API as C would.