These instructions assume you are playing Minecraft Pocket Edition version 0.12.1 or later. If you are playing an earlier version, be aware of the following changes:  Before 0.12.1, books do not require leather to craft, but they also have no use in the game. Before 0.3.0, books do not exist. Sugar cane is a green reed that grows near bodies of water. You can harvest it with your bare hands. Once you find some, consider planting your own back at your base so you have a permanent paper supply. Sugar cane grows on sand or dirt adjacent to water. If you don't have enough cane to make the amount of paper you'd like, you can make it grow faster with bone meal. Tap your crafting table and select the Paper recipe in the Decorations menu. This will turn three sugar cane into three paper. Each cow killed will drop 0, 1, or 2 pieces of leather. If you have Pocket Edition 0.11 or later, you can find it by fishing instead, but it is much less common there. The Book is another item in the Decorations section of the crafting table menu.

Summary:
Check your version number. Search for sugar cane. Turn three sugar cane into paper. Kill cows for leather. Combine paper and leather into a book.