Basically, "Cygnus X-1" is a song series by the band Rush that tells a story. The story is about a fictional character named "Cygnus". In the song series, Cygnus travels through space and discovers a black hole. He gets too close to the black hole and gets sucked in. But instead of dying, Cygnus actually enters a different dimension or universe.
The songs in the series continue to tell Cygnus' story as he tries to survive and figure out what's happened to him. The lyrics of the songs are really poetic and use a lot of metaphors and imagery to tell the story.
So basically, "Cygnus X-1" is a really cool story told through music, and it's about a guy who gets sucked into a black hole and ends up in a different dimension.