7. To make a layer style with your rusty pattern, first make a new layer. Now go to Layer>Layer Style>Pattern Overlay...Select your pattern among other patterns, it should be the last one at the bottom.
Step2: Finding the texture and adding it to Photoshop. Go to google and search for "Rusty Texture" when you find something you like copy it. (Right click on the image and click copy) I used an image from pixelperfectdigital.com, which can be found by clicking Here. Paste you image into Photoshop. After pasting the image into about, hold Ctrl and click on the image layer to select it. With the layer selected click Edit Define Patter click Here to see a video example.