What is it?
A gradient overlay is a combination of too (or more) colors that fade into each other, usually used as a background. An example of a gradient overlay is visible in the background of the graphic above.
How do I add one using Adobe Photoshop?
Adding a gradient overlay to your graphic is very simple.
1)Right click the paint bucket on the general window to the left and select gradient tool. If you do not see the paint bucket that means that the gradient tool is all ready selected. The icon for this tool is a rectangle that fads from white into black.
2)When you see it, click it and chose the colors you would like (chose the colors also from the general window, at the bottom).
3)After you have done this go to your photo and you will see that the cursor is a cross. Left click and hold down on the mouse button and drag your cursor along your image and release the button. Be default, the color you see where you first clicked your mouse will be the top one that appears on the general window and the second color will be the color underneath the first one , also on the general window
Congrats!! You've have succesfully added a gradient overlay.