It's roughly equivalent to High School diploma, and you could actually go to an American College/University with GCSE's, because you need a proof for secondary education, and GCSE's and High School Diploma are both secondary education qualifications. hope it helps.
SAT's
You call people living in Australia, Australians.
Australians call them "lifts", but the word "elevators" is not unknown.
Watermelon, Australians just have an accent.
i presume you mean do Australians call us poms? if so yes
KIDS
it is a veranda
We call them thongs, and yes, many Australians wear them.
If it is an outdoors "grill", it is probably what Australians call a Barbeque. With increasing frequency, it is sometime known by its brand name as a Webber.
Australians commonly call chickens "chooks" (rhyming with looks).
Aussies or Australians.
csicskák vagytoook.
Australians often refer to the remote countryside as the "outback." This term typically describes the vast and sparsely populated areas of the country that are far from urban centers.