About effects
After Effects includes a variety of effects, which you apply to layers to add or modify video and audio characteristics. For example, an effect can alter the exposure or color of a layer’s image, add new visual elements, manipulate sound, distort images, remove grain, enhance lighting, animate text, or create a transition.
You browse and apply effects using the Effects & Presets panel. You modify effect properties using the Effect Controls panel or Timeline panel or by moving effect control points in the Layer panel or Composition panel.
You can apply multiple instances of the same effect to a layer, rename each instance, and set the properties for each instance separately.
To see a video tutorial on applying and working with effects, visit the Adobe website at www.adobe.com/go/vid0228.
Because effects are implemented as plug-ins, you can install and use additional effects that parties other than Adobe provide. You can add a single new effect or an entire folder of new effects to the Plug-ins folder, which is located by default in the Program Files\Adobe\Adobe After Effects CS3\Support Files (Windows) or Applications/Adobe After Effects CS3 (Mac OS) folder. When After Effects starts, it searches the Plug-ins folder and its subfolders for all installed effects and adds them to the Effect menu and to the Effects & Presets panel. After Effects ignores the contents of folders with names that begin and end in parentheses; for example, the contents of the folder (archived_effects) will not be loaded.
Adobe provides many third-party effect plug-ins with After Effects. Keylight, Color Finesse, and Cycore FX plug-ins are installed by default with the After Effects application. The installers for some plug-ins install their documentation in the same directory as the plug-ins themselves. Documentation for Cycore FX plug-ins is available on the Cycore website: www.adobe.com/go/learn_ae_cycorefxdocumentation.
For more information on the various categories of After Effects effects, see Effect reference.
Animating effects
You animate effect properties in the same way that you animate any other properties—by adding keyframes or expressions to them. In most cases, even effects that rely on animation for their normal use require that you set some keyframes or expressions. For example, animate the Transition Completion property of a Transition effect or the Evolution setting of the Fractal Noise effect to turn a static effect into a dynamic effect.
Color depth
Many effects support processing of
image color and alpha channel data at a depth of 16 or 32 bits per
channel (bpc). Using an 8-bpc effect in a 16-bpc or 32-bpc project
can result in a loss of color detail. If an effect supports only
8 bpc, and your project is set to 16 or 32 bpc, the Effect Controls
panel displays a warning icon 
next
to the effect name. You can set the Effects & Presets panel
to list only the effects that support the color depth of the current
project. (See Set the color depth.)
Render order
The order in which After Effects renders masks, effects, layer styles, and transform properties—called the rendering order—may affect the final result of an applied effect. By default, effects appear in the Timeline panel and Effect Controls panel in the order in which they were applied. Effects are rendered in order from top to bottom in this list. To change the order in which effects are rendered, drag the effect name to a new position in the list. (See Render order and collapsing transformations.)
An effect applied to an adjustment layer affects all layers below it in the layer stacking order in the Timeline panel. (See Create an adjustment layer.)
Expression Controls effects
Expression Controls effects do not modify existing layer properties; rather, these effects add layer properties that expressions can refer to. (See Using Expression Controls effects.)
Preventing edge clipping with the Grow Bounds effect
Because an effect is applied to a layer, the results of some effects are constrained to the layer’s bounds, which can make the effect appear to end abruptly. You can apply the Grow Bounds effect to a layer to temporarily extend the layer for the purpose of calculating the results of other effects. This process is not necessary for newer effects, which tend to be 32-bpc effects.
Managing effects and effect properties with scripts
Paul Tuersley provides a script with which you can search compositions for effects and turn them on or off: www.adobe.com/go/learn_ae_pauleffecttoggle.
Paul Tuersley also provides a script that makes synchronizing changes to effect properties on multiple layers easier: www.adobe.com/go/learn_ae_pauleffectmultiplelayers.