PDO query dont work

PDO query dont work

i cant do an query.
This is my connection class
class DatabaseConnection {
private $host;
private $port;
private $dbname;
private $username;
private $password;
function __construct($host, $port, $dbname, $username, $password) {
$this->host = $host;
$this->port = $port;
$this->dbname = $dbname;
$this->username = $username;
$this->password = $password;
try {
$conn = new PDO("pgsql:host=$this->host port=$this->port
dbname=$this->dbname", "$this->username", "$this->password");
echo "PDO connection object created";
}
catch(PDOException $e) {
echo $e->getMessage();
}
}
}
$db = new DatabaseConnection('host','5432','eu','eu','eu123');
Query class
class Query {
private $query;
function __construct($query) {
$this->query = $query;
$sth = $db->prepare($this->query);
$sth->execute();
}
}
$query = new Query('SELECT * FROM users');
Thats it. I dont know how to display the query data, and also i would want
you to show me th RIGHT way to query and right way to show it. THanks!