Okay! Imagine the ground is like a big sponge. When it rains, the sponge soaks up water. The water table is like a line inside that sponge that shows how much water is there. Above the water table, the sponge is dry, and below it, the sponge is wet with water.
So, the water table tells us where the ground is full of water underground. If you dig down and reach the water table, it's where you can start to see and feel the water!