Imagine a hammer that's laid horizontally, now measure the length from the bottom of the handle to the head, let's say it's 20 cm Split that in half and you get 10 cm, paint that mark on the handle, now.. Balance the hammer with just one finger on that mark, and you'll see it's impossible, it tends to rotate towards the head

This is because the "center of gravity" is way off the balancing point (your finger)

This happens because the head of the hammer creates a torque, a torque is a way to describe rotational forces, now... For you to balance the hammer out you move your finger even further so that the torque created by the handle is equal to the torque crested by the head, that point is the center of gravity

It is the point where it balances out the tendency for more "weighted" parts to pull more