Hi you can search this on lynda.com this is perfect video training for the photoshop. you can also browse this on youtube for this purpose. here i would like to share with you some links which would be really helpful for you to apply gradient of your image.
www.woodfill.com/Lord_Tuts/tutorials/.../gradient_background
help.adobe.com/.../photoshop/.../WSfd1234e1c4b69f30ea53e41001031
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www.dummies.com/.../how-to-apply-a-preset-gradient </div><div>

www.dummies.com/.../how-to-use-gradient-maps-in-photoshop-cs6.


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