what is the use of Quantum Computing?

Let me explain "Why Quantum computers" rather than the uses of it , because quantum computers are certainly not meant for our day to day activities.

These computers are for high end purposes which our chip based computers wont be able to do. 
Moore’s Law was a forecast that was born out of an observation about the pace of chip technology. Moore predicted that the number of transistors on a chip would double every one to two years. His forecast held true for decades and helped power many of the advances that we’ve seen in computing since the 1960s, as computers have gotten smaller, more capable and ever more powerful.

But Moore’s Law has started to break down in recent years as the size of the transistors has shrunk down to near the atomic scale. Chip companies have had increasingly difficult times trying to pack more and more transistors on to each chip.

Quantum computing is nothing but performing the switch operation using atoms , just like how transistors did in semi conductor chips.