99% of a good photograph is down the the photographer (much in a similar way to how a good artist can make good art, even with the most basic of tools). However, having a "better" camera gives you access to a better set of tools in order to take your photos. A "better" camera may have changeable lenses, greater customisation of settings, and things like that. You'll also have the ability to control the flash, and the images will have larger dimensions which in turn gives you greater flexibility over cropping, etc.

It's important to remember, though, that having a good camera doesn't make you a goot photographer. Things like composition, etc., are important no matter which camera you have.

Hope that helps!