You want 90-95% of your diet to be comprised of "whole foods". Whole foods are foods made up of one single ingriedient. Think fruits, vegetables, seeds, nuts, meat, fish, and eggs. Basically foods found in nature without the need of human creativity.
Processed foods are foods we humans have created by adding together the tasiest parts of food found in nature. The problem with this is when foods are processed they lack the nutrition found in whole foods. For our bodies to function properly we need sufficient vitamins and minerals. Processed foods lack these essential nutrients while whole foods have them.