To use that you just need to Append the "Easy Hair 2.0.blend" file to your scene, selecting the "EASY HAIR" inside the "NodeTree" folder.

Draw curves on the surface of the object to establish the hair flow. (If you are using the mirror modifier you will gonna need to apply the "Visual Geometry to Mesh" and them convert it to curves again).

Now you will gonna need to duplicate the surface object, keeping the same topology and sculpt this to create a "Cage" mesh that will gonna be used to add height and volume to the hair.

Now add a Vertex Group to the surface object and go to the "Weight Paint" mode to paint in red the region where you want to add the hair strands.

To add the hair, first you will need to select the surface object, "Add>>Curve>>Empty Hair" to it, and add a Geometry Nodes modifier to this curves selecting the "EASY HAIR".

Load the surface object, the cage object and the curve that you draw on the surface object in the right inputs,

Increase the density until you see the hair strands and get satisfied with the density. Change the cage offset if you want to control the hair height and change the other settings.

This product comes with a real time hair shader applied to it so you can easily visualize the hair in the viewport, but you can change this by loading the material that you want for the viewport and final render.

You can continue editing the hair by using Blender Hair Nodes