You are not alone with such an issue. This could be because no one would have spoken to you and educated about sex related matters.
Knowing and learning sex education will definitely be helpful as you grow and mature. Look this as an opportunity to learn than having assumptions of what you could have heard from some matured sources in the environment you live.
Next Steps
since this is a chapter in biology, talk to your teachers who can help and guide you to understand better.
Health Tips
Refrain talking about this to peers as you may be waste time with I'm matured and unproductive discussions