Maori stone carving

Today we started sand papering our stone carvings. I am not up to that part, but some of my friends told me what they had to do. I ask myself why we had to use sand paper but the teacher that was the leader of stone carvin, said we use it to make the carvings smooth. As I said I am not up to that part, but when I get up to sanding my carving then I will know what to do.