Hi Michael, the easiest way to use Flow is the "curve to curve" variety where you use a base curve and a target curve, check out here for some examples on that:
That can work for a cylinder shape as well, using a line as the base curve and a circle as the target curve as in the 3rd example.
For doing a sphere you'd need to use "Surface to surface" flow where you instead choose a base surface (which is usually a plane sitting under your objects) and a target surface rather than curves.
