Dynamic in-game object creation and manipulation

[Tomi]

Hello everybody!
I'm still new here and the Lazarus is a bit new for me. I would like make a small game with Lazarus, in which the player can put down balls in the window on the mouse coordinates - but my code doesn't work. Here is:

unit Unit1;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, mouse;

type

  { TMainWindow }

  TMainWindow = class(TForm)
    procedure FormClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;

type TBall=class(TObject)
  private
  public
    constructor makeit(xplace,yplace: integer; itspic: Tbitmap);
end;

var
  MainWindow: TMainWindow;
  ballpic: TBitmap;
  aball: TBall;

implementation

{$R *.lfm}
constructor TBall.makeit(xplace,yplace: integer; itspic: Tbitmap);
begin
        xplace:=getmousex;
        yplace:=getmousey;
        itspic:=ballpic;
end;
//end;

{ TMainWindow }

procedure TMainWindow.FormClick(Sender: TObject);
begin
      aball:=TBall.makeit(getmousex,getmousey,ballpic);
      MainWindow.Canvas.Draw(aball.xplace,aball.yplace,aball.itspic);
end;

procedure TMainWindow.FormCreate(Sender: TObject);
begin
  ballpic:=TBitmap.Create;
  ballpic.LoadFromFile('ballbmp.bmp');
end;

end.

And the error messages:
Projekt fordítása, Cél: kepfutidoben.exe: Kilépési kód: 1, Hibák: 3, Tippek: 3
unit1.pas(26,24) Hint: Value parameter "xplace" is assigned but never used
unit1.pas(26,31) Hint: Value parameter "yplace" is assigned but never used
unit1.pas(26,4 Hint: Value parameter "itspic" is assigned but never used
unit1.pas(50,36) Error: identifier idents no member "xplace"
unit1.pas(50,49) Error: identifier idents no member "yplace"
unit1.pas(50,62) Error: identifier idents no member "itspic"

Somebody can help me to solving this problem? I would like placing ball objects at runtime.