Photo Manipulation 101

[IQ89]

What would be some first steps toward learning how to digitally manimulate photos on-line? Is there software you need to buy? Or when you sign up with a PhotoBucket-type site do they provide everything you'll need?

Just as an example, let's say I wanted to create a photo of David Sklansky with a mohawk haircut for an avatar. Now I wouldn't want to merely use a colored pen to scribble it in, that would look kinda cheesy. I'd like to be able to digitally cut and paste some feature (like a haircut) from one photo onto another.

Thanks