Question regarding Double pointers.

It was told to me that if you passed a double pointer as an argument to a function :

int function1(type arg1, (type**) &arg2)
{
....
}

That you are passing the address to the pointer which, which is assumed is pointing to something else. And, that by doing so, you allow the function to point that double pointer to something else.

My question is, if it is a temporary storage of the address to the pointer that the function is receiving dictated no more than by (type**), how would you re-assign it to another address. Would you have to declare a new pointer in the function and assign it the (type**) address to it, then point it to something else?

And my last question (part II) is where does pointers really come into play and are helpful/useful?

Thanks much