Create a stored procedure as:
Create Procedure AddDetails
(
@visitorname varchar(50),
@subjectdescription varchar(500),
@date datetime,
@time datetime
)
AS
BEGIN
declare @visitorid int, @subjecid int
BEGIN TRAN
insert into visitors
values(@visitorname)
set @visitorid = scope_identity()
insert into Subjects
values(@subjectdescription)
set @subjecid = scope_identity()
insert into visitorSubjects
values(@visitorid,@subjecid,@date,@time)
COMMIT
END
Now pass parameters from front end to insert data in all the three tables.