link the scenes togather

hi there

please i need your help i have finished 4 different scenes in opengl & c++
but when i try to link all of them in one class
i want the scene to appear then after i press on key board char
the second scene appears
i read about timer funtion but i don not know how to use it

note : i create the scene in different classes and all of them are 3d expect the first scene 2d :frowning: