What to do with Vertex Normals

[stevenlin111]

I have a obj file which has Vertex Normals. I know that Vertex Normals are used for lighting. The only thing I can find on the internet about Vertex Normals is calculating the vertex normal which is already given in the file. What am I supposed to do with the Normal and the face?

[mattdesl]

The normals are used when calculating lighting, among other things.

Illumination Model