Reynolds number equations?

I have a definition of Reynolds number as being Re = pLovo/n (p=density, Lo=radius?, vo=speed, n=viscosity).

I also have the equation f(Re) = Fd/pLo^2 vo^2. I understand that this is another dimensionless number to do with scaling. If so, how?

I'm not sure what the term Fd is when doing this scaling & also how, when a sphere is going through a liquid this term is found to be f(Re) = 6(Pi)/ Re, or is this last one just an example to answered in a separate question?