How to store all vertex normals within a shader file (Unity)

I am new to shaders in Unity. I would like to create a shader for an AR application. Therefore I need to compute the normal for every vertex. In addition to that I need to know which vertices are neighbors, such that I can store them. So can anyone help me out here? Do I need an unlit shader? How do I get all the vertices of my mesh? How can I store them? Do I need shaders or is there a different way to do this in unity?