The best thing, @Chris2040 , will be to read everything you can in the Help pages. There are so many things that will broadside you if you don't!
But short answers are that you have Instant Book (IB) turned on. That will be why the reservation came in. Well done making it work! It is such a mess if you don't.
You can turn it off in the edit section by selecting "all guests must send a reservation request"
Always stay on top of your calendar! If you cannot host a certain day or week or month, block those off.
Airbnb collects from the guest immediately. You are paid the day after check-in, but when you are new, payment comes much later. This is to prevent fraud. You can look that one up in Help.
As to knowing whether Airbnb has the money, they nearly always do. I have not had a problem myself. You can always look at Upcoming Payouts in Earnings to check.
Hope that helps, and all the best with hosting!