Textures.com

1. Create an account on the Textures.comwebsite if you haven't already

.2. Download it. It should go into your DOWNLOADS folder

.3. Find the downloaded file in your Downloads folder

.4. Open it by dragging it to the Photoshop icon  on your dock.

Avoid opening your file with the wrong application by dragging it to the PS icon on your dock. Or...Right-Click and choose "Open With: Photoshop"

5. Use the Window Menu > Arrange > 2 Up Vertical option to view the two files side-by-side

6. Use the move tool to drag the texture into your project file

7. TILE it If it doesn't cover the entire BACKGROUND.

You can also drag the closed file icon from the downloads folder onto your Texture Name file but you will have to rasterize it afterwards.