Apples are about 80 - 85% water. Dissolved in this water is a fair bit of sugar. They are about 13 - 14% sugar. So that takes up about 97% of the apple. The same is true of almost all fruits, by the way. The last few percent is made of fiber, a bit of fat, and trace amounts of protein, minerals and vitamins. You can see a complete breakdown at the US Department of Agriculture National Nutrient Database for Standard Reference.