A Photoshop action is a series of steps that are performed in Adobe Photoshop and can be used and re-used with a simple click. An action is created by manually performing those series of steps once and recording them in an ATN file.
You can record your own custom actions or download actions created by other users from the Web.
Installing Actions in Photoshop
By default, the Actions panel displays only the actions that come with the application.
To add the actions that you have downloaded, for example from one of your RA video courses, follow these steps:
Step 1. Open the Window menu in Photoshop and make sure the Actions panel is checked:
Step 2. In the right upper corner of the Actions panel, click the Options menu and choose Load Actions…
Step 3. Within the pop-up window, navigate to the folder where your new action is located, click on the .ATN file (your new action) and press the Open button:
Step 4. Now this action (or a set of actions) has been added to your Actions panel in Photoshop. To play an action – simply select it and press the Play button at the bottom of the Actions panel:
Adobe Helpdesk page dedicated to Photoshop actions and Actions panel: About actions and the Actions panel.