I will try to explain.
Take the entire mad list
{
{ { "a", "b" , "c"}, { "d", "e", null } },
{ {"x"}, null },
{{"y"}},
{ { "z","p"}, {} }
}
and try to imagine it to be an unidimensional array. For this we can break it up with commas. Thus we have an array of 4 elements. Now take the first element of the said array { { "a", "b" , "c"}, { "d", "e", null } } - which again looks like an array and can be broken up by commas. Thus we have a nested array of two elements inside the first element - i.e the elements a[0][0] and a[0][1]. Since we are only concerned with a[0][1] we take a closer look at it i.e { "d", "e", null } . This again is an array of three elements a[0][1][0](="d"), a[0][1][1](="e") and a[0][1][2](=null) - our required answer.
Hope I have been clear enough.