-- 1 - glass
-- 2 - black
-- 3 - red
Slots = {
    {
        {2, 3, 3, 2},
        {3, 0, 0, 3},
        {3, 0, 0, 3},
        {2, 3, 3, 2}
    },
    {
        {3, 0, 0, 3},
        {0, 0, 0, 0},
        {0, 0, 0, 0},
        {3, 0, 0, 3}
    }
}




for layer = 1, #Slots do
    -- From 1 to number of elements in Slots (2)
    for line = 1, #Slots[layer] do
        -- When program starts line == 1
        -- From 1 to number of elements
        -- in line number `line` (7)
        -- On the second time line == 2
        for elem = 1, #Slots[layer][line] do
          -- When program starts elem == 1
          -- Then Slots[line][elem] == Slots[1][1] == 1
          -- On the second time
          -- elem == 2
          -- Then Slots[line][elem] == Slots[2][1] == 1
          slot = Slots[line][elem]
          if slot ~= 0 then
              turtle.select(slot)
              turtle.placeDown()
          end
          turtle.forward()
        end

        for turt = 1, #Slots[line] do
          turtle.back()
        end
        turtle.up()
    end
    turtle.turnRight()
    turtle.forward()
    turtle.turnLeft()
    for i = 1, #Slots do
       turtle.down()
    end
end