In fact, you can read the corresponding article "Whoever learns to die will no longer have a enslaved mind and can ignore all constraints and coercion" to give you a better understanding.
Learning to die here means looking at the things and relationships you are involved in from the perspective of a deceased person. That is to say, under strong pressure, bring out the worst consequences of your own death, and find the meaning of life and the motivation to move forward without fear from failure. To be honest, it is difficult. It is difficult for people to control their emotions very well, but those who can control themselves are all successful.