All blocks have different destroy times, or levels of time that it takes 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). Also, there CAN be blocks in creative mode that are uncraftable or unreachable or unobtainable in survival.