Creating a normal map in zbrush?

Hi I would like to create a normal map in zbrush from one of my high poly models. This model is NOT unwrapped. I was told I could unwrap the low poly version in blender and then import it back in and use the high poly to create a normal map. My question is how do I import the low poly .obj into zbrush and how do I set it up to where zbrush uses the high poly one to bake on to the low poly one that I just imported. Thanks!