I am a history education student, so I can sort of tell where you're coming from, as occasionally in class I'll be called on to teach a topic I may not know that much about, or haven't studied up on in a while.
Well, for the nerves part…I used to be really bad with handling pressure, and I could never give a speech prepared or otherwise. What I did to fix that, and this is gonna sound really strange, is get into magic. I learned to good card tricks and started doing them for my close friends, and then for people i knew, and then for strangers. The pressure you have on you when doing a magic trick is intense. People are going to be burning your hands and you have to stay calm. At first the stage fright will be bad, but you'll get comfortable with it. and one of the best things is that someone will ask you to do a trick when you're not necessarily planning on doing one, so you'll kind of have to run through something that you know on the fly.
And one of the best things I learned is that by trying to be perfect I just mess up more. If I'm relaxed and just go with it I find I do better at both the lessons and magic. Basically, if you're confident in what you're saying a doing, the audience is going to accept it, but if you doubt yourself, the audience will doubt you as well.
Like I said, it's a strange way, but it worked for me...
As for the topics, all I can tell you is what I can find on google, so I figure that won't be much help.