@Noor0 I'm not sure if I fully answer your questions, but I'll try.
You can send a pre-approval to a guest who has made an inquiry. The have 24 hours to accept, and if they do, then the reservation is confirmed. After 24 hours, if the guest accepts your pre-approval, then you have to accept the reservation. You can send as many pre-approvals as you want. The first guest who accepts a pre-approval gets the booking. You can read more about pre-approvals here:
https://www.airbnb.com/help/article/838/what-is-a-pre-approval
On your second question, you should never allow a potential guest to come to your place without having a confirmed reservation. This is for your privacy and security. Here's what Airbnb says about site visits:
https://www.airbnb.com/help/article/47/what-should-i-do-if-a-guest-wants-to-see-my-place-before-book...
I hope this helps, but if not, please reply and I'll try to help some more!