It all starts with some training. There is a lot of training available online. Here are some sites you can look at. If these prove to be helpful please reflect that in rating.
thanks
Eric

http://www.layersmagazine.com/category/tutorials/photoshop
http://graphicssoft.about.com/od/photoshop/l/bllps5out.htm
http://www.photoshopsupport.com/tutorials.html