As you work on a project that contains a number of layers, you many times apply effects to various layers that add visual interest to your image. Each of the effects, such as the Drop Shadow or Outer Glow effect, have a variety of options that you can use to control the appearance of the effect. For example, you can set the distance of a drop shadow effect or the spread of an outer glow effect.
Each time you apply an effect to a layer, the option settings revert to their default values. To apply an effect using the same option settings in one layer to another layer, you could write down the values from the first and then set them all individually in the second layer. There is, however, an easier way. Simply go to the Layers panel, [ctrl]-click (right-click in Windows) on the layer whose effect you want to copy, and choose Copy Layer Style from the pop-up menu. Then [ctrl]-click (right-click in Windows) on the layer you want to paste the layer style to and select Paste Layer Style from the pop-up menu.