Advanced Driving on a 5spd, need help?

So. A few questions. Firstly, speed shifting. My friend did it today. When he was driving, he mentioned shifting without touching the clutch. Except I didn't believe him and wasn't letting it happen on my prelude. But he did it on my bronco, and he got her pulling HARD. What exactly is it, how do you do it, any thing it damages, and why don't racers use this manuever? He told me to do somr research and here I go. Also, question about a sensitive throttle. I find starting my prelude in 2nd is much easier and harder to stall in. But can you stall if your in too high of a gear and you aren't giving it gas? I've never really felt like trying it. Lol