To animate a property is to change its value over time. In Premiere Pro, effect properties can be animated by assigning keyframes to them.
A keyframe marks the point in time where you specify a value, such as spatial position, opacity, or audio volume. To create a change in a property over time, you set at least two keyframes—one keyframe for the value at the beginning of the change, and another keyframe for the value at the end of the change. Premiere Pro then creates a gradual change in values between keyframes, called interpolation.
You can work with keyframes either In the Timeline or in the Effect Controls panel.