There exist various ways to generate a spiral in parametric design. I think this method is one of the most simple ways to understand and follow step by step. It can be further developed by controling density and deformation of spiral geometry. Tutorials below show the construction logic of spirals with parametric contorls.

Click Here for Tutorial PDF Download : BASIC SPIRAL

Click Here for Tutorial PDF Download : DENSITY SPIRAL

Click Here for Tutorial PDF Download : DEFORMING SPIRAL