How do I know the different allowable parameters for win32api calls when I'm using VFP.

For example: (code snipped from Microsoft VFP support)

ln_current_window=GetWindow(ln_current_window,2)

This performs a get next window handle.

In the MSDN Platform SDK the command is detailed as follows:
(some text removed for clarity)

HWND GetWindow(
HWND hWnd, // handle to original window
UINT uCmd // relationship flag
);

Parameters
hWnd
Handle to a window. The window handle retrieved is relative to this window, based on the value of the uCmd parameter.
uCmd
Specifies the relationship between the specified window and the window whose handle is to be retrieved. This parameter can be one of the following values: Value Meaning

GW_CHILD The retrieved handle identifies the child window at the top of the Z order, if the specified window is a parent window; otherwise, the retrieved handle is NULL.

GW_ENABLEDPOPUP Windows NT 5.0 and later: The retrieved handle identifies the enabled popup window owned by the specified window

GW_HWNDFIRST The retrieved handle identifies the window of the same type that is highest in the Z order.

GW_HWNDLAST The retrieved handle identifies the window of the same type that is lowest in the Z order.

GW_HWNDNEXT The retrieved handle identifies the window below the specified window in the Z order.

GW_HWNDPREV The retrieved handle identifies the window above the specified window in the Z order.

GW_OWNER The retrieved handle identifies the specified window's owner window, if any.

* My question is how would I determine that GW_HWNDNEXT is equal to 2 in VFP? And how do I deal with similar situations using other API calls.
I have experience in all FoxPro versions but most API examples are for C++ and VB which just confuse me more. Any help with this would be appreciated.