Adobe Photoshop/Gradient Tool
The Gradient Tool is the more complicated brother of the Paint Bucket Tool. It works by having one color of fill fade into the other. It has many features, and we will only cover the most common here.
Right click on the paintbucket button and click on "Gradient Tool". Now, set your background and foreground colors. Click and hold were you want the gradient to begin and move your mouse to were you want it to end. Then let go of the mouse button. you should now have a basic gradient.
More Advanced gradient useEdit
Right click on the picture of a gradient on the top of the screen (Under "Photoshop") and you should get a menu. Click on one of the stoppers on either side of the gradient and pick your color or click one of the options above it. then click ok.
You can also change how the gradient acts. Look to the right of the picture off the gradient and you will see 5 or so pictures. These change how the gradient acts. The picture gives a pretty good idea of what it will change.