everyone can contact you and send you an inquiry before booking.
Anyone who can't book instantly has to send you a booking request ( not the same as inquiry)
It depends on your booking requirements setting, for example, if you require your guests have reviews and recommendations from previous hosts then they can instantly book. Others have to send you a request.
yes @David4201 you can turn off "instant booking" option, but your listing may be placed low in theb search results (depends how much competitors you have in your area)