1. Grab an image you'd like to use, I'm going to take this image from Aethereality.net.
2. Go all the way to Layer -> Duplicate Layer.
3. And it should look a little darker than before.
4. Grab some colours you want to use, got for C5B4A2 for the skin colour. And then pick another colour for the hair and then so on.
5. Now what you do it zoom in about %500. And then carfully take the Paint Bucket and start to colour in his face with C5B4A2. You'll probably get something like this:
But don't worry that's part of the tutorial.
6. Now go all the way to Layer -> Then change the Bleeding Mode to Multiply.
7. Then you'll probably get something like this:
But we aren't done yet.
8. Although it look like that, you don't have to repeat all those steps, just take you Paint Bucket Tool and start carefully filling it in with colours.
9. Now you should be done by now colouring in your image. Then you can add other effects like back grounds and brushes and such. =)
I hope your tutorial was helpful. =) Now you are done, if you are lost, stuck, or something went wrong please go back and look again. Or post your questions at the forum.