Double-click on the ATN file with a filename that corresponds with your version of Photoshop. For example, if you are using Photoshop CC, then you should double-click the "Pastel Colors by SparkleStock (Photoshop CC).atn" file.
Go to your Actions panel (Window > Actions) to find the actions. If you do not see the actions, click on the panel menu (top-right corner of the Actions panel) then click Load Actions. Browse for the ATN file then click Load.
Retro Film Actions:
In the Actions panel (Window > Actions), click on the "Play All Effects" action.
Go into your History panel (Window > History) and select an effect.
Adjust the layer opacity to change the strength of the effects.
Light Leaks
Drag and drop (or go to File > Place) any light leak image into your document.
Change the blending mode to Linear Dodge. You can also experiment with other blending modes such as Screen, Overlay, Linear Light, etc.