@Jean511 When you get a booking request for certain dates, those dates will automatically block for that request. The host then has 24 hours to Accept or Decline, and in the meantime, before doing that, you can respond to the request if you want to ask them some questions, or most hosts respond by thanking them for their request, saying you're looking forward to hosting them (assuming you don't feel any red flags go up about the guest), then hit Accept. You really shouldn't decline unless you really don't want that guest, you get penalized by Airbnb for declining too often. The reason the calendar gets blocked is that the guest has 24 hours to complete payment before the booking is confirmed.
There's no reason you shouldn't be able to respond to a guest request- it's pretty straighforward. You get a notification that you have a request, then you go straight to it and respond. You don't access that by clicking on the dates on the calendar.
I admit I don't really understand what you're doing exactly that is not working properly, unless there's some tech glitch with your account.