Sex, death and the meaning of life are all big and complicated topics and will be different for everyone, so no one answer can capture what they mean for everyone. So, here's one way to think about them.
Sex is about the physical closeness, the pleasure, and connection that two people can have when they give and receive affection, love, and pleasure from one another.
Death is the end of life, when the body stops working and people are no longer alive. It can feel sad and scary, but it's also a natural part of life and is necessary for living things to keep growing, changing, and evolving.
The meaning of life is whatever you want it to be. Some people think life is all about finding happiness and joy, while others think it's about making a difference in the world. The important thing is that each person finds their own way and their own meaning by living the best life they can.