How does a lever make work easier?

It technically does not make work easier, you really do the same work. But if you meant force applied, you do apply a smaller force. Since you may apply the force further from the fulcrum (point of rotation) than the load is therefore the force required to lift the load is smaller. This is true because of torques which is force X distance from fulcrum, therefore to apply the same torque if you increase distance your force subsequently decreases.

Returning to the comment that work is constant, since you are applying a force further from the fulcrum, the distance you have to push is further; therefore, due to Work = Force X Distance, you still do the same work since even though your force decreased, distance had increased.

Although the lever does not change the work, it does** make the work easier. You are more concerned with the force that you have to apply than with the mechanical work input and output, so you are expending less energy by applying less force. I think this is what you mean by "easier". If simple machines did not make life "easier", we would never have bothered to invent them!