Complex sentence: In 1982, a large alien spacecraft stops directly above Johannesburg, where investigators discover a population of sick and malnourished extraterrestrials, identified derogatorily as "prawns", which they confine to District 9, a government camp outside Johannesburg.
Split into simpler sentences: In 1982, a large alien spacecraft stops directly above Johannesburg. When investigators enter the ship, they discover a population of sick and malnourished extraterrestrials, identified derogatorily as "prawns", which they confine to District 9, a government camp outside Johannesburg.