I started creating online courses recently and while I can perform well under no pressure in the comfort of my own home while taking as many cuts as I need to get out what I want to say, I have trouble explaining things live to an audience.
So far I've gone up twice in front of 70 or so people for only 60 seconds to announce my course. It's material I know very well.
The first time was pretty bad. Not a total tank, but lots of fumbling around and eventually saying things in a way that wasn't very clear at all.
The second time was a bit better. It had a rocky start for the first 3-4 seconds (aka. life times when you're up there) but I pulled it together and something vaguely coherent came out. I kind of just went into auto-pilot mode with confidence because it's something I wrote out like 20 different ways when I was working on my introduction video.
I didn't study a script for either of them but I practiced what I wanted to say in my head while I was walking to the venue. Probably not the best plan, but I've never been strong at having to memorize long blocks of text, it's just not how my brain works.
I think you do have to study hard to give a good presentation but being able to improvise is critical, especially if you plan to take questions at the end.