question

how to use photoshop plugin

Hey- I appreciate your brevity, but in this case I might need more info to tell you what you need. To answer your question, you simply put your "Plug-In" in the "Plug-Ins" folder (located within the "Adobe Photoshop _" folder on your Hard Drive). Then, next time you launch Photoshop, you'll have access to the plug-in (most likely from the bottom of the Filter menu).
That's the quick answer and I hope it suffices.
Photoshop comes with a bunch of Plug-Ins. Take a look in that folder. Many are filters, Some are little helper applications designed by Adobe or someone else. Your scanner needs a Plug-In (placed in the Import/Export folder) in order to access it from within Photoshop. If you download a Plug-In that claims to work in Photoshop from somewhere, make sure it's compatable with your version number, and read and follow the directions that came with it. They should tell you where to put it and how to use it.