What is the shadow zone and why does every earth quake have one

Need the answer asap,and not too complex please.

To understand the shadow zone, you need to understand the two most basic seismic waves; P and S waves.

P waves move the fastest and are compatible to the motions of releasing a stretched out slinky or a Newton's Cradle. P waves tend to go through all states of matter, most importantly, liquid as well as solid (but they get deflected in the phase change).
S waves on the other hand move slower and are more like whipping a rope thats tied to a wall. They do not go through liquids and only through solids.

Now what a shadow zone is, a zone where seismic waves of a certain type do not show up on the other side of the earth. This is because the outer core is liquid and therefore, S waves do not pass and P waves get deflected.