"The more precisely the POSITION is determined,the less precisely the MOMENTUM is known" -Werner Heisenberg

This is probably the most difficult part in Quantum Physics. Briefly speaking, Heisenberg's Uncertainty principle describes that the more precise you know about the position of a particle, the less precise you know about the momentum, and the more precise you know about the momentum, the less precise you know about the position. Why is that? First lets consider an example:

"If there is a particle, such as an electron or a neutron, in this case we use an electron, moving through space and time, It is possible to characterize its motion by telling you its position and what its velocity is (to be precise, its momentum)."

Something particularly strange would occur if we try to measure its momentum and position.
In Classical Physics, you can measure this 2 things to more or less, infinite precision. Momentum and positions are nothing in Newtonian Mechanics.
In the Quantum Physics, measuring things exactly are completely dissolved. In HUP, p (momentum) and q (position) cannot be measured precisely and accurately. It was because that when you make a measurement, you are actually disturbing the system. The quantity of uncertainty are dependant:
dp x dq > h / (2pi) = h/ ( 2 x pi )
For example, if I measured p exactly, the uncertainty in q, dq would be infinite in order to keep the answer constantly contant.