First, the answer:

To get the ID of the last entry, just use mysql_insert_id()

$sqlinsert1 = mysql_query("INSERT INTO 'destinos' VALUES('', '$destino')");
$id_destino = mysql_insert_id();

$sqlinsert2 = mysql_query("INSERT INTO 'entrada_pt' VALUES('', '$id_destino')");

One remark:

This code does not make sense.

$another_id = mysql_query("SELECT * FROM 'destinos' WHERE destino = '$destino'");

The mysql_query() function does not have the ID of the record inserted, but a pointer to a result set.

To use your 2nd query, instead of mysql_insert_id() , you would need this:

$sqlselect1 = mysql_query("SELECT * FROM 'destinos' WHERE destino = '$destino'");
$row = mysql_fetch_assoc($sqlselect1);
if ($row)
   $another_id = $row['id'];

The most important:

  

No one should be using the mysql_ functions in PHP anymore!
  They are insecure * and obsolete, and are no longer available from PHP 5.5.   Use the mysqli_ !

* Actually the functions themselves are not insecure, but are used insistently in the worst way. There are people who exchange lib , but still put PHP variables directly inside SQL. Ideally, you should only use binding .

The mysql_ * functions are obsolete and it is recommended to use mysqli or PDO. In this question has a list of arguments to DO NOT use them.

To get the last inserted id use the function mysql_insert_id ()

$sqlinsert1 = mysql_query("INSERT INTO 'destinos' VALUES('', '$destino')");
$id_destino = mysql_insert_id();
$sqlinsert2 = mysql_query("INSERT INTO 'entrada_pt' VALUES('', '$id_destino')");

You can use yes !! The only difference is to change mysql_ by mysqli _.... and put the connection link, as below.

include 'conexao.php';

//$conn é a variavel de conexão utilizada em conexao.php

$sqlinsert1 = mysql_query("INSERT INTO 'destinos' VALUES('', '$destino')");

$id_destino = mysql_insert_id($conn);

$sqlinsert2 = mysql_query("INSERT INTO 'entrada_pt' VALUES('', '$id_destino')");