How does a single fixed pulley help when lifting a load?

A single fixed pulley (attached to a fixed point overhead) changes the direction of the force — letting you pull down to lift a load up — but it does not reduce the amount of force required; you still must pull with a force equal to the load's weight. To gain a mechanical advantage (reduce the force needed), you use a movable pulley or a combination of pulleys (a block and tackle), which trades reduced force for a longer length of rope pulled. Understanding that a fixed pulley redirects force while movable/multiple pulleys multiply it is a frequently tested simple-machine concept.