By applying an effect to a track, you apply the effect to all media files on the track.
Click a track name and the track name will be highlighted with a green rectangle, which indicates that the track is selected.
Once the track is selected, select an effect and drag it to the track name to apply the effect to the whole track.
The effect will take effect on all media files on the track. You can then edit the properties of the effect.
To access the properties of the effect on a track, right-click the track name and click Edit.