Okay kiddo, today let's talk about a special way of saying "he" or "she" that some people use when they don't know if a person is a boy or a girl, or if they want to be inclusive for people who don't identify as either.
Instead of using "he" or "she," they use a special word called "they." This is called singular "they" because it doesn't refer to a bunch of people, just one person.
So, let's say I'm telling you a story about someone I met, but I don't know if they're a boy or a girl. Instead of guessing and saying "he" or "she," I can just use "they." For example, "I met someone today and they were very nice." See, I didn't assume anything about their gender, so "they" is a good word to use.
Some people might think it's weird to use "they" this way, but it's actually been around for a long time. Shakespeare even used it in some of his plays!
Using singular "they" is just one way of being respectful to people who might not fit into traditional boy/girl categories, or who might not want to reveal their gender. It's important to be kind and inclusive to everyone, regardless of their gender.