It will be something like below. You can use SCOPE_IDENTITY()to get the last autogenerated identifier with the scope, which is this stored proc in this case:
create procedure NameOfYourProcedureHere
as
begin
insert into custlogin(custusename, custpassword)
values ('','')
insert into custinfo(custid, custfirstname, custlastname, custaddress)
values (SCOPE_IDENTITY(), '', '', '')
end