Photoshop plug-ins are program module files which add functionality to Photoshop. The plug-ins must be installed in specific directories. The main location is the "Plug-ins" folder under the Photoshop install directory. For Windows users, the default path is "C:\Program Files\Adobe\Photoshop 7.0\Plug-ins".

Photoshop also allows the user to specify a secondary directory from which it should look for plug-ins. This secondary plug-ins directory can be specified in "Preferences" and the directory can be any location on the computer.

Photoshop checks for plug-ins to load only when it starts up. So, when new plug-ins are installed, Photoshop may need to be restarted if it is already running.

Once installed, the plug-ins will be available in one of many menu items. There are several types of plug-ins ... filters, import (acquisition), export, automation, and others. The most common plug-ins, filters, show up under the "Filter" menu. Import and export plug-ins show up under "File->Import" and "File->Export" menus. And the automation plug-ins show up under the "File->Automate" menu. The user documentation for each plug-in should describe where to find the plug-in and how to use it.