use ds_grid to make game menu issues

*what i try to do*
my main page should have START SETTINGS and EXIT ,when i press key Z key on setting , it should go to setting page. but I have no idea about why my code didn't work. it still stay on main page.
*create*

image_speed = 0;
var up, down, accept, back;

global.pause = true;
global.view_width = camera_get_view_width(view_camera[0])
global.view_height = camera_get_view_height(view_camera[0])
display_set_gui_size(global.view_width, global.view_height);

global.key_left =...

use ds_grid to make game menu issues