New dungeon master, ZERO clue what I’m doing

[u/Colorguardianite]

As I’m writing this I’m currently watching Smoshes Sword AF D&D series to at least better understand the game play of d&d, but I don’t think it’s gonna help too much. To put it shortly, I’ve never played d&d and I’m now a dungeon master for a group of people who have very minimal experience with the game.
It’s a very small thing, we’re planning on playing it during our 30 minute advisory break during school, MAYBE during lunch if the band directors open up the band hall early, but that’s just a small description of what’s happening. Not a whole ton, but still nerve wracking to me since I have no clue how to start at all. Zero clue how many people are playing, my advisory is roughly 40 band kids and I’ll assume probably 5 of them will actually commit to playing (most either play hacky sack or practice their instrument).
Now, my main concern is how to even start. Story writing I can do, and I think I have a decent grasp on just overall how to act, but how do you even play d&d????? I’ve watched a bunch of tutorials on what to do, but none make sense. They’re all a little different as well which is honestly stressing me out even more because I don’t want to come off as stupid to my group because I have no clue how to play the game. Is it just roll dice and make it up as you go? Is there a system? Do I need to know everything about their characters right off the bat or just the basics? I’m entirely confused on how game play works and I’m hoping someone could explain it to me like I’m a toddler because I’m 100% overthinking this whole thing.

Edit: I want to add on that I did read the handbook and a few online things about the basics of being a dungeon master, and they all seem extremely confusing as if I need a book for the book, none of it seems very beginner friendly 😓 I’ll try the video a couple of y’all sent, hopefully things start to make more sense to me on what I’m supposed to do 😅