Did you look in the manual under the [man]session[/man] section?
$_SESSION is simply a superglobal array with associate keys. Store data in the array and you can retrieve it in successive pages.
What you're trying to do is assign a value to the $pass1 variable with an index of '$pass'. Not only is this incorrect, but '$pass'] is not equivalent to the value of [b$pass - PHP does does not replace variables with their values in singe-quoted strings.
Though you won't be using the function, the man page for [man]session_register[/man] shows how to use the $_SESSION superglobal to store data in the session (look at the code example).