Best software for graphic novels?

Everyone's got to start somewhere, and for me, I want to start getting into comic-book style art. Mainly, it's for drawing the scenarios in my spy/spy co-story I'm working on with my writing partner. For personal entertainment purposes. I've always been interested in this, and now, getting my first job at 16, I want to raise the money up to buy the best, easiest to learn software to draw graphic art. Much like this: http://24.media.tumblr.com/61177e75a583cb74072ad0e...

(Just an example I found for one of my favorite fandoms.)

I own a Macbook. What software would you recommend?

Thanks in advance to anyone trying to sincerely provide tips and help to my question.