How to add data to the database using mysqli in php, phpmysqli_PHP tutorial

$mydb = new mysqli('localhost', 'username', 'password', 'databasename');

$sql = "INSERT INTO users (fname, lname, comments)

VALUES ('$_POST[fname]', '$_POST[lname]', '$_POST[comments]')";

if ($mydb->query($sql) == TRUE) {

echo "user entry saved successfully.";

} else {

echo "INSERT attempt failed" ;

}

$mydb->close();