Can explain how its working?

Question

Somebody can me explain whats going on and how its working?

void func (int *arr, int n1, int n2)
{
int i, j;
for (i = 0; i < n1; i++)
for (j = 0; j < n2; j++)
printf ("%d\n", *(arr + i * n2 + j));
}

int
main (void)
{
int b[3][4] = { { 1, 2, 3, 4 }, { 5, 6, 7, 8}, { 9, 10, 11, 12 } };

func ((int*)b, 3, 4);
return 0;
}