without being given any more context, i would assume it means is the (i-1)-th power of . so the first row should all be 1's. this kind of matrix is called a Vandermonde matrix.
you'll probably arrive at a better understanding if you try it first for n = 2, and n = 3. try to factor the result into binomials.
if you are clever, and figure out (guess) the general form, you can actually prove it by induction on n.