2. Once you've opened it up, go to the Fill tool.

3. You'll notice at the top there it looks like this:

Change the Foreground to Pattern.

4. When you change it to Pattern, right beside it you'll notice a pattern. Click on it and change it to the pattern you want.

5. After you've done all that, all you have to do create a new layer (Layer-New-Layer). Then fill in your pattern on your new layer so it looks like this:

6. It looks horrible, right? That's why you're going over to the layer mode. It's usually right beside the Opacity.

Click on the Layout Mode and a dropdown menu should present itself.

7. You can experiment on which mode you like with your pattern. I selected Soft Light though.

8. After that, you can save it. This is what mine turned out like:

If you have any questions, just post!