php - $_SESSION is not insert into value -

i want make web using php. in login form, i've make process go ‘menu.html’. in process go menu, did process name ‘auth.php’. in ‘auth.php’ want make $_session index $_session['id_user'] id_user table ‘user’, in ‘menu.html’ when want access doesn't work session. have idea solve it?

maybe i'll show pictures understand:

you have start session before use of it.

for example:

session_start(); $id_user = $_session["id_user"];