How to digitally color/draw?

I'm opening an online store for tshirts and I'm making my own designs. I'm not very good at drawing by hand so I was wondering if you guys know any programs/apps that can digitaly draw and color. I'm trying to make designs like the ones on colorw0w 's instagram, heres the link~
http://instagram.com/...m/colorw0w
I have an iphone and a windows pc. And is adobe photoshop easy to use?

There are dozens of free and inexpensive graphics programs for drawing and painting.
If you know what you are doing it can be easier and faster than traditional media.
If you don't know what you are doing it is much more difficult than putting pencil and paint to paper.

If you don't know how to draw, I don't see the advantage of using digital media. It can help you draw more perfect circles, and keep the paint inside the lines, but thats about it.
If you can't draw on paper, you will not be much better on the computer.

Photoshop is difficult to learn to use properly. There are simpler programs that can do much the same things. Just Google 2d graphics programs, or paint programs, etc.