Photography freelance beginner...?

[cali_girl]

I am hoping to start my freelance photography very soon but the thing is I've done my research on cameras and its gotten down to two cameras the Nikon D90 and the Nikon D300. I've noticed that they are pretty much the same. But thats not really my concern, my concern is figuring out apertures. Does anyone know of a good photography book I can invest in that will help me a lot with mostly all aspects of photography? I take pretty decent pictures already but I want to take great pictures. I have an eye for things but need to learn how to capture exactly what I want. I also want to learn a lot about night photos. Soooo suggestions please. I would really love them.