Blocks are the basic unit in Minecraft: Pocket Edition. They make up the entire environment for the game. Every blocks face has 16x16 pixels to generate an image. It is possible to collect these as resources, to recreate another form of the block, or use them to build structures. Most natural blocks are weak, un-blast resistant and don't look good so that's why most people don't build houses out of dirt.
All blocks have different destroy times, or levels of time that it take to break them, and when they break, they emit different sounds like ping! for glass, crunch! for dirt, or a boom! sound for stone and ores. They are often use to make structures that provide some sort of fortification or entertainment. Currently, there are about 36 blocks, along with about 8 objects (not including tools).