Vaccine testing?

How do Vaccination companies do their vaccination testing/trials?
I just read an article about GSK and their Pandemrix H1N1 vacc, and it said "GSK says the final H1N1 version was tested in trials involving around 3,600 patients, including children, adolescents, adults and the elderly, before it was rolled out."

Well how the smurf do they get the candidates? Do they just stroll into hospitals with their top hats and act like theyre handing out candy? Did they start conducting these trials when the pandemic first started, and they had sick people sign up?

I don't really understand how parents would just sign theyre kids up for some new crap to be pumped in their brain. What if they die? Did they get paid for it lol?