Firstly, it helps you expand your vocabulary. As you read, you'll come across new words in context, which makes it easier to remember them. Secondly, you get to understand Spanish grammar better. You'll see how sentences are structured in different tenses and forms. Also, reading stories exposes you to different writing styles and cultural references in the Spanish - speaking world.
One way is to make summaries of the stories in Spanish after reading them. This forces you to understand the main ideas and use the language actively. Also, try to imitate the writing style you see in the stories when you write your own short paragraphs in Spanish.
It could be an expression of defiance or a very unique way of stating something related to a personal story that involves black identity. But without more context, it's hard to be very specific.
One example could be a story where a black person is constantly underestimated in a workplace. They keep getting passed over for promotions despite their excellent work. One day, they finally stand up for themselves and say 'kiss my black ass' to the unfair system and then start to tell their story of how they've been marginalized in the workplace. And that's their 'black kiss story' of fighting for equality in the work environment.