How do I write a Control Panel Applet?

STRINGTABLE { 
//the "title" of applet #1 
10, "Demo Current Time #1" 
//the description of applet #1 
11, "Shows the current system time..." 
//the "title" of applet #2 
20, "Demo Current Time #2" 
//the description of applet #2 
21, "Shows the current system time..." }

12 ICON applet1.ico //the icon for applet #1 
22 ICON applet2.ico //the icon for applet #2

library myapplets;
  uses SysUtils, Classes, Windows, cpl //a unit in Delphi 3,
       frmApplet1 in 'frmApplet1.pas',
       frmApplet2 in 'frmApplet2.pas';

{ Demo control panel application
  based off of a link to "Creating Control Panel Applets with Delphi" by Ted Houts
  cleaned up & posted on tek-tips by Glenn9999 }

{$E cpl}                 //changes the extension to CPL from DLL
{$R cp_resource.RES}     //resource built containing the icons and string for the applets in this .CPL
const
  APPLETS_COUNT = 2;     //the number of applets (items that show up in Control Panel)

var
  Frm_Applet1 : TFrm_Applet1; //applet #1
  Frm_Applet2 : TFrm_Applet2; //applet #2
//This procedure puts the action of opening applet dialog boxes into one place

procedure OpenDialogBox(DlgNo,PageNo : Integer);
{
  This project has 2 applets (dialogs) which are roughly identical.
  If zero is passed, open the first applet; otherwise, one should be passed,
  but just in case, any other value for dialog number will open the second applet.
}
  begin
    if DlgNo = 0 then
      begin
        Frm_Applet1 := TFrm_Applet1.Create(nil);
        // this line puts the icon resource associated with this form in control panel
        // to the VCL form itself
        Frm_Applet1.Icon.Handle :=
               LoadIcon(hInstance, MakeIntResource( (10 * (DlgNo + 1)) + 2));
        Frm_Applet1.ShowModal;
      end
    else
      begin
        Frm_Applet2 := TFrm_Applet2.Create(nil);
        // this line puts the icon resource associated with this form in control panel
        // to the VCL form itself
        Frm_Applet2.Icon.Handle :=
               LoadIcon(hInstance, MakeIntResource( (10 * (DlgNo + 1)) + 2));
        Frm_Applet2.ShowModal;
      end;
   end;

{
CPlApplet is the callback function that processes all messages from
"controlling application", i.e. Control Panel
}

function CPlApplet(hWndCPL : hWnd; iMessage : integer; lParam1 : longint;
         lParam2 : longint) : LongInt stdcall;
  begin
    case iMessage of
      CPL_INIT :
      //first message, sent once: this is the time to create global objects
        begin
          Result := 1;
          exit;
        end;
      CPL_GETCOUNT :
      //second message sent once, return the number of applets supported by this file
        begin
          Result := APPLETS_COUNT; //number of dialog boxes supported
          exit;
        end;
      CPL_INQUIRE :
     //Filling in the CPLINFO record with resource information. NOTE resource
     //file has clever IDs so as to make the code based on the dialog number,
     //see cp_resource.rc. lParam1 is zero-based dialog (or applet) number.
     //lParam2 is a pointer to a CPLINFO record that's filled with the applet
     //information, including "lData," which can point to application-specific
     //stuctures. Fill the record and return 0.
        begin
          PCplInfo(lParam2)^.idName := (10 * (lParam1 + 1)) + 0;
          PCplInfo(lParam2)^.idInfo := (10 * (lParam1 + 1)) + 1;
          PCplInfo(lParam2)^.idIcon := (10 * (lParam1 + 1)) + 2;
          PCplInfo(lParam2)^.lData := 0;
          Result := 0; //handled, returning zero
          exit;
        end;
      CPL_NEWINQUIRE :
     //This has an identical function to CPL_INQUIRE except that it requires
     //a different format set for data.  See above for notes.
        begin
          PNewCplInfo(lParam2)^.dwSize := sizeof(TNewCplInfo);
          PNewCplInfo(lParam2)^.lData := 0;
          PNewCplInfo(lParam2)^.HIcon :=
               LoadIcon(hInstance, MakeIntResource( (10 * (lParam1 + 1)) + 2));
          LoadString(hInstance, (10 * (lParam1 + 1)) + 0,
               @PNewCplInfo(lParam2)^.szName, sizeof(PNewCplInfo(lParam2).szName));
          LoadString(hInstance, (10 * (lParam1 + 1)) + 1,
               @PNewCplInfo(lParam2)^.szInfo, sizeof(PNewCplInfo(lParam2).szInfo));
          PNewCplInfo(lParam2)^.dwHelpContext := 0;
          PNewCplInfo(lParam2)^.szHelpFile[0] := #0;
          Result := 0; //handled, returning zero
          exit;
        end;
      CPL_SELECT :
      // obsolete message supported for backwards compatibility.
        begin
          Result := 0;
          exit;
        end;
      CPL_DBLCLK :
      //user has double-clicked one of your icons in the control panel, respond here
        begin
          OpenDialogBox(lParam1,0);
          Result := 0; //handled, returning zero
          exit;
        end;
      CPL_STOP :
      //sent once per applet, do form shutdown code here.
        begin
          if lParam1 = 0 then
            Frm_Applet1.Free  //user has closed Applet #1 form
          else
            Frm_Applet2.Free; //user has closed Applet #2 form
          Result := 0; //handled, returning zero
          exit;
        end;
      CPL_EXIT :
        begin //sent once this is the time to free global objects
          Result := 0; //handled, return 0
          exit;
        end;
      CPL_STARTWPARMS : //CPL_STARTWPARMSA, CPL_STARTWPARMSW
        //sent when applet started via rundll32.exe this .CPL will support an
        //integer param to indicate the page number, default to page one
        //if invalid
        //lParam2 is the parameter string passed in the command line.
        //lParam1 and return value are the same as CPL_DBLCLK
        begin
          OpenDialogBox(lParam1, StrToIntDef(String(lParam2),1));
          Result := 1; //handled, so return 1
          exit;
        end;
      else
        begin
          Result := 0; // return 0 to indicate that this message isn't processed
          exit;
        end;
    end;
end;

//as required export CPLApplet by name
  exports CPlApplet name 'CPlApplet';

begin
end.

"C:\Program Files\Borland\Delphi 3\Bin\brcc32.exe" cp_resource.rc
"C:\Program Files\Borland\Delphi 3\Bin\dcc32.exe" myapplets.dpr
rem To Deploy to the system directory if necessary.
rem copy myapplets.cpl C:\Windows\system32

rem clean up old files
del *.~*
pause

rundll32 shell32.dll,Control_RunDLL "myapplets.cpl", @0