Do simple machines reduce the amount of work?

By simple machines, I assume you mean machines powered by muscle but using leverage such as levers, screws, block and tackle devices. Is that what you mean? If so, these devices increase something called "mechanical advantage".

Start with levers. The usefulness of a lever depends on where the fulcrum is placed. If the fulcrum is in the centre of a lever such as with a see-saw, there is no mechanical advantage at either end. That's why kids of similar weights can suspend the kid on the other end of the see-saw up in the air just to be rascals. Now if the fulcrum is closer to one end than to the other, the person farther from the fulcrum can exert more force than the person closer to the fulcrum. Think of a crow bar. One inserts an inch or two of the bar at the point where one wants to apply force. Pushing on the other end of the bar (perhaps two, three, four feet away) exerts a lot of force at the other end. The same effect allows you to lift a car with a jack. You push down a foot on the jack handle and the jack platform rises perhaps half an inch.