If it pertains to dark skies in a non - fictional sense, it's about the importance of reducing light pollution. Many places are losing their natural dark skies due to too much artificial lighting, and efforts are being made to reverse this trend.
It could also be some specific local story. Maybe in a certain town, there was an event that happened during the night in the past and has been named the 'Dark Skies' story. But without more details, it's hard to be more precise.
The 'Dark Skies' real story may vary. If it's about the film, it's a horror - type story of a family in distress. They face odd happenings that seem otherworldly, like things moving on their own and strange noises at night.