Questions from the naïve

Okay, I have a lot of things I'm unsure about I just need clarification. What is the fertile window that's on my <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a> calendar? Why do women discharge and what is it? What is ovulation? What's it like giving a blowjob? I've never done it and my boyfriend wants me to but I'm not sure if I want to or not. Thanks ladies!