As for the first question, you're trying to access the 3rd element, of the 2nd element of the 1st element of the jagged array:
jaggedArray[1][2][3]
As for the error, a 3D array expects the same number of elements in each element of a dimension. Let's say, for simplicity's sake, that you have a 2D jagged array, a rough representation of what that looks like in memory would be:
First row -> 2, 3, 4, 5, 6, 7, 8
Second row -> -4, -3, -2, -1, 0, 1
Third row -> 6, 7, 8, 9, 10
You can see that each row is seen as a different array, and can therefore differ in size. A multidimensional array, however, does not have this property. It needs to be filled completely:
Column : 0 1 2 3 4 5 6
------------------------------------
First row : 2, 3, 4, 5, 6, 7, 8
Second row: -4, -3, -2, -1, 0, 1
Third row : 6, 7, 8, 9, 10
Your table is missing some cells, which makes no sense. You need to use the same number of elements per dimension.