How to talk to men!!!!!?

I'm freshman he : Preston : is a junior. We have talked a little bit but only when the teacher has told us to. I'm not good with boys. Ive never had a boyfriend or anything like that. I can't just walk up and say hi because I can't keep a good convo up. And we dont have any homework in that class so that wouldn't work. He sits two people behind me on the row next to me so talking to him is against the flow. Please help :$ flirting or talking tips