If you want to pay for it, Photoshop is a wonderful program.
http://www.adobe.com/products/photoshop/compare/
If you want to do basic photography edits, Photoshop Express is great.
https://www.photoshop.com/express/landing.html
But if you want a program similar to Photoshop, but for free, try the GIMP.
http://www.gimp.org/
Buuuut, if you want a program like Photoshop with a little less for, try Paint Shop Pro.
http://www.corel.com/servlet/Satellite/us/en/Product/1184951547051#versionTabview=tab1&tabview=tab0
Or if you want a program meant for photo editing, try Paint.NET.
http://www.getpaint.net/