@Annie1372 The registration is for hosts who rent to a guest who stays for less than 31 days, as opposed to listing your property for month/long term stays. So you do not have to register if EVERY guest stays with you for longer than 31 days, but you do have to register if you accept a guest for a weekend, a week, 10 days or any length of stay less than 31 days.
It is not counted by the number of days that you rented over the year.