How does conception happen? What are some common types of STDs and how are they transmitted? What are some common methods of preventing pregnancy, how do they work, and how effective are they? Hopefully you already know the basics, but if not, go dig around. Even if you aren’t currently sexually active, this information is important when exploring (and talking with others about) the issue of abortion. If you have children of an appropriate age, make sure they know the basics too.
If you want a quick (yet detailed) overview of fertilization, pregnancy, and development, Crash Course has some pretty good videos.