What makes these type of helicopters fly? 
These are called coaxial helicopters, but it seems very weird that how can these helicopters fly? I had a toy helicopter like this and something that I noticed was when it's blades were rotating, they rotate in the opposite direction. They both rotates with the same angular velocity so far. My question is, when the upper blade produces the thrust force then, the lower blade beneath also produces the thrust force in the same direction. Then what's the use of this second blade beneath If the first blade is doing the same work?
Rather This should intruppt the amount of air that the first blade want to throw downwards and push the helicopter downwards as well because of the obstacle i.e the second rotating blade, if it want to move upwards then then anything should not intruppt the air, if this happens then the forces will get cancelled and the helicopter will remain stationary but this doesn't happen at all, rather it's even more stable while it levitates. How is this possible? And why do we need that second blade while the normal single blade would also do that work very easily as the huge original single blade helicopters does?
Why are these toy helicopters made like these? Why the coaxial helicopters are uncommon in the real life, is there any reason that the large helicopters can't be made like this? I've gone through some articles on the internet and noted some conclusions according to them regarding this but that didn't helped me a lot to understand.
 A: 
Then what's the use of this second blade beneath If the first blade is doing the same work?

It's simpler to keep stable.  With a single main rotor, there will be some drag force.  This force will create a torque that will tend to spin the vehicle in the opposite direction of the rotor.  By having two rotors in opposite direction, the drag and torque from each cancel.  The helicopter is rotationally stable at all RPM without any additional active components like a tail rotor.

Why the coaxial helicopters are uncommon in the real life, is there any reason that the large helicopters can't be made like this?

Aerodynamically a single rotor is more efficient than two smaller ones.  A coaxial shaft has losses and compromises over a single simple rotor shaft.  These are minor on a light toy, but would cost a lot on a full-sized vehicle.  It's cheaper and simpler to have a single rotor and an anti-torque system like a tail rotor.
This is the same reason you don't see full-sized quad-rotors flying people around either.  It makes the control system simpler, but at a loss of efficiency.
