How do I talk to my daughter about ?

My daughter is almost 9 years old and she knows the word so I attempted to explain the concept to her. She knows about periods and why Mommy has them. The one time I tried to explain the difference between boys and girls I ended up pulling out the encyclopedia and she lost interest. I am a single mother so I don't have any male support on this issue so I'm scared and confused as to how and when to go about this. I don't want her learning from friends at school because as we all know she won't get the truth. What do I do?