Layer styles let you quickly apply effects to an entire layer. In the Effects panel, you can view a variety of predefined layer styles and apply a style with just a click of the mouse.

The boundaries of the effect are automatically updated when you edit that layer. For example, if you apply a drop shadow style to a text layer, the shadow changes automatically when you edit the text.
Layer styles are cumulative, which means that you can create a complex effect by applying multiple styles to a layer. You can apply one style from each style library per layer. You can also change a layer’s style settings to adjust the final result.
When you apply a style to a layer, a style icon appears to the right of the layer’s name in the Layers panel. Layer styles are linked to the layer contents. When you move or edit the contents of the layer, the effects are modified correspondingly.
Once you choose Layer > Layer Style > Style Settings, you can edit the settings of a layer’s style or apply other style settings or attributes available in the dialog box.
Drop Shadow
Specifies the distance of a drop shadow from the layer’s content. You can also set the size and opacity with the sliders.
Glow (Outer)
Specifies the size of a glow that emanates from the outside edges of the layer’s content. You can also set the opacity with the slider.
Glow (Inner)
Specifies the size of a glow that emanates from the inside edges of the layer’s content. You can also set the opacity with the slider.
You can apply special effects to a layer, hide or show the styles in a layer, and even change the scale of a layer style (for example, decrease or increase the size of a glow effect). It’s easy to copy a style from one layer to another.

If you don’t like the result, press Ctrl+Z (Command + Z in Mac OS) to remove the style, or choose Edit > Undo.
Bemærk:
You can also drag the style to the image, where it is applied to the selected layer.
You can edit a layer’s style settings to adjust the effect. You can also copy style settings between layers and remove a style from a layer.