In discussing working with Two-Dimensional Arrays, please explain the following with the most simple, begiinger level, easiest to understand explaination (no coding example nessecary):

With a two-dimensional array, for which operations would you use nested "for" loops and for which operations would you use a single "for" loop?

When performing an operation on a given row, which index is fixed and which index is used as the looping variable?

When performing an operation on a given column, which index is fixed and which index is used as the looping variable?