Completly new to this....and very nervous

You can work wherever you are offered a job.

You don't specialize in school You study everything, and you'll probably hear that nursing is holistic--we treat the whole patient (true, but we still whine when we get floated to a different unit!) As a nurse, you can apply for a position in the field you prefer. You might apply to the ortho floor, or you might be more interested in a rehab facility. Actually, you apply through HR, but if you let them know you have an interest in a particular area, they may have openings, there. Or you may just get offered a position wherever they need you most. You can pursue certifications in the specialty of your choice, but most of them include work experience in that field as part of the qualification.
It's not like the way a doctor decides to specialize as an orthopedic surgeon and trains toward that.
Depending on your job market, you may find it easier to take whatever job you can get, with an eye toward transfering into your desired specialty. Still, if you're offered a job in Oncology, say, and turn it down, they may have other places they can use you.
I took a job on the unit where I already worked in an unlicensed capacity, not so much because I was facinated by neurology, but because I knew the people and knew my way around. My fondness for neuro patients grew after I started working there--although I've always had an interest in the psychological aspects of the brain, which has some application in my work.

May I also suggest you check out the Student forums (there's a tab at the top of the page). You can post anywhere that interests you, but you'll find a lot advice and commiseration from others in the same boat.