Okay kiddo, so let's start with the United Nations - it's like a big group of grown-up leaders from different countries who get together to talk about important things that affect people all over the world.
Now, sexual orientation and gender identity are two things that are very important to some people. Sexual orientation is who you are attracted to - so some people are attracted to boys, some people are attracted to girls, and some people like both or neither. Gender identity is about how you feel on the inside - some people feel like they are a boy and some people feel like they are a girl, and some people feel like they are somewhere in between or something else entirely.
Sometimes, people who are different from what is considered "normal" by society can face discrimination or harm, which means they are treated badly just because of who they are. This is not okay, and the United Nations wants to make sure that everyone is treated fairly and with respect.
So, the United Nations talks about sexual orientation and gender identity to make sure that everyone's rights are protected, no matter who they are attracted to or how they identify themselves. They want to create a world where everyone is accepted and can live their lives without fear of harm or discrimination.