click 2d button to display object

hi guys,
I’m really very confused
need an idea or a simple example of how i could achieve this. i

click a button and i load/display first object.
click second button i load/display first and second object…that idea

i have something like this

void buttoncallback()
{     
Draw3D();
}
void display(){/*
	 *	Clear the background
	 */
	glClear( GL_COLOR_BUFFER_BIT |
			 GL_DEPTH_BUFFER_BIT );

	/*
	 *	Enable lighting and the z-buffer
	

	/*
	 *	Draw the 3D elements in the scene
	 */
	Draw3D();

	/*
	 *	Disable depth test and lighting for 2D elements
	 */
	glDisable(GL_DEPTH_TEST);
	glDisable(GL_LIGHTING);

	/*
	 *	Set the orthographic viewing transformation
	 */
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(0,winw,winh,0,-1,1);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();

	/*
	 *	Draw the 2D overlay
	 */
	Draw2D();

	/*
	 *	Bring the back buffer to the front and vice-versa.
	 */
	glutSwapBuffers();
}
main(...)
{
        .......
        glutDisplayFunc(Draw);
	glutReshapeFunc(Resize);
        .....
}

a short snippet would really help thank you