why I couldn't add song in my playlist for ipodtouch4

I just restored my ipodtouch. I didn't sync my entire song to itunes.

I put song in my folder at computer. And I copied those songs to itunes into playlist, for example: American-English song. But I couldn't see anysong in my ipodtouch in good orders.

I could manage those folders at the first time I use ipodtouch, but I couldn't control these folder anymore after I reinstore my Ipodtouch4.

Please tell me what should I do to put songs in my playlist for ipodtouch4.