I booked a hotel for three days. If I didn't arrive on the first day, but went to the hotel the next day, what would happen to the original room? I have to pay for two days. ...

You reserve a hotel for three days. If you don't check into the hotel on the first day, your order will be invalid, and there will be no order for you when you arrive at the hotel the next day. It is best to suggest that if you can't get to the hotel on time on the first day, call the hotel in advance and make some changes.