"On the beach" is actually on the sand... "at the beach" is kind of in the general area. I'm doing this lesson while at the beach, yet not on the beach.
Uk English = on the beach
What is the difference between 'estou' and 'sou'?
Estar - a momentary state. Ser - a definitive state. So you always "está" in a place, never "é" in it.