I have absolutely 0 experience with this. Have Googled, but there's lots of stuff, plus I suppose the first 10 results pages are sponsored affiliate sites, similar to "top 10 hosting providers". So, can anyone point me in the right direction? What exactly am I looking for?

Looking for an easy and, preferably, free way to host a live tutoring session to up to 500 students. So they can post questions in the last 15 minutes, or so - and get answers right away. Teacher needn't see the students (text communication from them is acceptable), but it would be preferable for the students to see the teacher - live.

Which platform to use for this?

Also, how to get the subscriptions - so they are verified? My first idea was to use WordPress and "newsletter" subscription model, like explained here:
https://io.bikegremlin.com/12061/wordpress-mailing-lists/

That would create a verified list of real emails, that can be confirmed with all the parents if needed (think that would be wise).

Another question is about doing it for the money - in case it goes well I think it could be a good idea. Working with larger groups, not just 1-on-1 on-line tutoring. In that case, a platform that is paid for would be more acceptable. But that would also require a more efficient way of tracking paid subscriptions, mailing list is probably not good enough for that (would require lots of manual updating I suppose).