<form action="" method="post">
 Pilih Kategori:<br>
 <select name="category[]" multiple="multiple" size="5">
  <? foreach(array('Music','Sport','Travel','Lifestyle','Business','Entertainment','Food') as $a): ?>
  		<option value="<?=$a?>"><?=$a?></option>
  <? endforeach; ?>
 </select><br>
 <input type="submit" name="choose" value="Choose!">
</form>

<?
	if(isset($_POST['choose'])){
		$cat = $_POST['category'];
		if(empty($cat)) echo 'Anda belum memilih kategori';
		else echo 'Pilihan anda adalah: '.implode(', ',$cat);
		echo '<hr />';
	}
?>

array(3) {
  [0]=>
  string(5) "Sport"
  [1]=>
  string(6) "Travel"
  [2]=>
  string(9) "Lifestyle"
}