samsung's big Galaxy S23 event is tomorrow and all will be official, likely with pre-orders to follow shortly after they wrap up the presentation. With pre-orders going live and the event kicking off, that means the reservation period that is currently open will close. In other words, this is your last chance to get the reservation bonus of up to $100 for your pre-order.
To recap this reservation thing, just understand that Samsung does this every time they launch a phone. Because everything they make leaks in a grand scale for weeks and weeks leading up to its official reveal, they kind of assume you know what's coming and let you “reserve” one (here). Reserving a Galaxy S23 or Galaxy S23 Ultra, in this situation, does not mean you are committing to buying one. Instead, you are letting Samsung know that you have some level of interest in what they are about to announce.
As a way to thank you for showing interest, they often offer a bonus that you get if you end up pre-ordering. For the Galaxy S23, that bonus is an extra $50 credit to be used alongside a Galaxy S23 or Galaxy S23 Ultra to pick-up accessories or other devices, like a Galaxy Watch 5 Ultra or case or battery pack or fast charger. They'll likely offer a credit to everyone who pre-orders, but by reserving you get the extra $50.
You can technically get up to $100 in credit if you tell Samsung you are interested in both their new phones and a Galaxy Book. However, you'd then have to also buy the Galaxy Book to get the extra $50. At least that's how it has worked in the past.
There is no obligation to buy with a reservation, you simply put your name on the list for pre-orders and if you decide to buy, get an extra $50 to spend. Not bad.