When you apply an effect to a layer, the Effect Controls panel opens, listing the effect you just applied and controls to change the property values for the effect. You can also work with effects and change most effect property values in the Timeline panel. However, the Effect Controls panel has more convenient controls for many kinds of properties, such as sliders, effect control point buttons, and histograms.
The Effect Controls panel is a viewer, which means that you can have Effect Controls panels for multiple layers open at once and can use the viewer menu in the panel’s tab to select layers.