Inherent to classical physics are the ideas of position, velocity, momentum, energy of particles and it claims to be able to precisely measure each of these physical propeties. In fact, by experience we see and observe our world in terms of particles having a fixed location at a given point of time.
But, if some fine day, we get down to experimenting with small particles ( if they can be called particles ) like electrons, protons etc. and try to somehow measure their position at a given point of time, we find that we cannot do it. And the difficulty is not that we don't have the technique or ability to do so, but that we are trying to do something which, in the world of quantum physics ( the real world ) is meaningless and impossible. It is searching for something which doesn't exist !
The uncertainty principle tells us that if we try to give a classical interpretation to quantum mechanical systems and try to measure the position and momentum, we can never get a level of accuracy more than a certain value. There will always remain uncertainties in the measurements, the product of which has the minimum value of the order of the Plank's constant.