So I'm planning to have the 'Birds and the bee' talk with my younger sister

My sister is 9 years old and I was thinking to teach her about sex education. I know my parents won't talk about this or even say the word 'sex' from their mouth but as an older sister it is my responsibility to teach her about this. One problem is that I don't have any ideas how to approach this conversation to her. It would helpful if you guys give me some advise about it.