Before and After

Step 1
Open up your picture in Photoshop and go to Layer >> New >> Layer to add a new layer.

Step 2
Now click the gradient tool on your side bar. There should be a new tool bar on near the top of the screen that looks like this.

Step 3
Now click the little arrow as shown in the example and pick whatever gradients you have.

Step 4
Now next to that is this:

You can choose which ever to use on your picture. If you hover over them, it tells you what they are. They are as follows: Linear Gradient, Radial Gradient, Angle Gradient, Reflected Gradient, and Diamond Gradient. I will be using the Linear Gradient. You can choose the other settings on the gradient tool bar as well if you want.

Step 5
Now with your mouse click on the upper left hand corner outside of the picture. Now you don’t have to start where I do but this is how I’m doing it. You can start your gradient anywhere.

Step 6
Now drag your mouse across the picture while still clicking to the bottom right hand corner. When you release your mouse a gradient should show up on your picture.

Step 7
Now click F7 so that your Layer Palette shows up and change the top layer to whatever Blend Mode you want. I set mine to Screen.