Take a hard card board.
Firstly we need to paste many layers of cardboard to all the sides and the bottom of the box.
Provide insulation that helps in slowing down in the heat loss.
Make sure that the insulation is even in all sides of the box.
Now take the aluminium foil and paste it at the bottom of the box and paint the sides of the box in black because black colour is a good absorber of heat .
When the paint is dried completely in the box . A mirror should also paste in the box so that light rays(Sunlight) get reflected .Your Solar cooker is ready
Put anything like popcorn , grains in the box at the bottom it will get cooked in few minutes.