<?php
  if ( empty( $_POST ) ) {
?>
<form name="newaddgenre" action="newaddgenre.php" method="POST">
  <label for 'genre'>Genre: </label>
  <input type="text" name="genre_name"/>
    <br/>
  <button type="button" class="btn btn-primary">Submit</button>
</form>
<?php
} else {
    $user = 'root';
    $pass = 'mysql';
    $db = new PDO ('mysql:host=localhost;dbname=musicdb', $user, $pass);
    $form = $_POST;
    $genre_name = $form[ 'genre_name' ];
    $sql = "INSERT INTO genre (genre_name)
    VALUES (genre_name)";
    $query  = $db->prepare( $sql );
    $query->execute( array( ':genre_name'=>$genre_name) );
  print_r( $_POST );
}
?>