It's way too complicated to do on this forum, but there are hundreds of PS tut's online…here are some from my favorites.

www.photoshopdrawings.com/tutorials/scribbling-pencil/index.php

www.good-tutorials.com/

www.graphic-design.com/Photoshop/
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This is an incredibly complicated topic that couldn't possibly be covered in a yahoo answer, so I'll point you to some tried, true, and eternally useful pages on the subject:

www.furiae.com/tutorials.php

www.conceptart.org/forums

http://itchstudios.com/psg/art_tut.htm

http://features.cgsociety.org/story_custom.php?story_id=3338&page=

Another excellent resource is a magazine geared solely towards the digital art community. It's called Imagine FX and can be found in most Borders and Barnes and Noble stores. It'll cost you 15 bucks a pop if you get it off the shelf (It's a british magazine, so the import tax gets factored in to the list price) or about 100 dollars for a subscription. It sounds expensive, but it's well worth the money. Some of the best digital illustrators I've ever seen, and many that I am a big fan of have contributed tutorials, brush sets, step-by-step photoshop files and many more things to the magazine– not to mention the free software demos and PDF back issues included with every magazine. It's the best 15 bucks a month I've ever spent.
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personal experience

There are millions of answers.
The best is. Buy a pencil and paper and begin drawing.
Leave that computer for what it is.
If you only work on a computer never your hearth and soul will get into that work.
Start with buying a Wacom tablet and you will see what is possible.
References :