Is there a way that i can use letsEncrypt for my local domain name e.g hot.spot, so the users each time will not see the certification error?
and if so, is there a tutorial where i can see for doing it?
In short, no.
You can use LE certificate for your login page, but it needs to have valid public hostname, otherwise LE won’t give you certificate for it. But it still will not help you with users having some https website as their homepage and getting errors when redirected to your hotspot.