You want to make sure everyone has read Chapter 9 from Player Core, which goes over the basics of the game. 90% of it will be fairly old hat for people coming from 3.x and 5e, but it does contain the core system differences from those games.
Menace Under Otari, the adventure in the Beginner's Box, is explicitly a tutorial dungeon designed to teach both game masters and players the mechanics of the system. Rusthenge is another purpose-built "first adventure", though it's not explicitly a tutorial, and has less system guidance for the GM. I've also heard that Dawn of Frogs is a good introductory adventure, that in some ways does a better job of introducing the system than Menace does (but I don't have it/haven't read it).AyeSpidey, on Reddit, also has an introductory adventure they wrote, that you can find on Pathfinder Infinite.
Crown of the Kobold King is a good early adventure, but it's a port of a Pathfinder 1e adventure, so I don't think it's the best choice for everyone's first time.
One thing that's key for the game is making sure everyone knows what their characters do. As people who've played something other than 5e, I assume you're all used to that, but I've seen a lot of people drop into the subreddit complaining that, as GM, it's too much work for them to know how everyone's characters work. The culture of "I don't know how to play, I just let the guy hosting things tell me what to do" falls apart here.
PF2e is fairly heavily based in D&D 3.5, though, even if the core 'engine' is different. What's markedly different, though, is how the game treats characters/creatures and the "character builder" game. The game itself includes a lot of guardrails that functionally prevent character-based hyper-optimizing. Character power bands are strongly level-based, and level is a direct, if mildly fuzzy, measure of character power. Many players grind against this at first, because they're used to finding wacky interaction effects and loopholes that just make them functionally a higher level than their character sheet says. Instead, the game rewards cooperation, tactics, and outplaying the other side of the table.
A lot of people playing the system like it for for how it just surfaces a bunch of 'paper buttons' for them to press over and over again, and how it provides a rigid, predictable style of play. I'm happy for them that the game provides them tools to generate the experience they want, but I've also found that these players have a more generally dim view of what other kinds of experiences the system can enable. It's a wildly flexible system that can power a huge range of table experiences, if you so choose. The key is understanding what is core to the game and it's balance, and what is just "good ideas suggested by professional designers".
The four core pillars of the game are the proficiency system (T/E/M/L), the degrees of success system, the action constructs, and the feat-based modular character design. Everything else is a default recommendation for adjudicating an outcome.
