Do you mean on top  of the other on the y-axis or the frames  actually
stacked on each other? If you mean the y-axis one you can do it a
few ways the simplest is this:
public class KFrame /*just an example name*/ extends Frame
{
public KFrame(String name, int x, int y)
{
super(s);//calls the frame  constructor that excepts the name of the
frame
setSize(x,y);//sets the Frame size to x,y
setLayout(new GridLayout(1,2));//it might be (2,1) I forget, I
//don't use GridLayouts that much
add(new Panel());//you can use a pre-defined panel, this is just an
// example. Be sure to use Panels, not Frames, you can't add Frames
add(new Panel());

setVisible(true);//this just makes the window visble
}
}