Don't get PhotoShop. It works geat, but it's expensive unless you're a pirate.
I use
Paint.NET. It's freeware. Started as a college project mentored by Microsoft and still continues development with some of the original students to this day. It was originally designed to replace the Paint that came with Windows. No clue why it never got implemented. I'm not sure if it's better than PhotoShop (though it's been compared to it) or has all the bells and whistles it does, but it's pretty awesome for 100% off.