It is very easy. All you need are the following supplies:
- the cutting board you want to refinish
- fine sanding paper/block
- mineral oil
- brush to apply it with (or rag/sponge, etc.)
Simply sand the board to remove surface imperfections. Sand until your heart's content. Then rinse the board off.
Next apply a thick coat of mineral oil, and rub it in, all sides. Apply as many coats as you'd like.
Let it sit and soak for a while.
Wash, and - voila! - like new! Recycling at it's finest!