Follow the instructions below to add a song to a playlist from your Android device:
Touch the triangular menu button to the right of an album, artist, song or genre, and touch Add to playlist. You can also add the currently playing song from the Now Playing screen by touching the menu button to the right of the song title and touching Add to playlist.
Touch the name of the playlist to add the song to it.
You've now added the song to a playlist.
Currently, Google Play has a limit of 1000 tracks per playlist.
To rearrange songs in a playlist while using your Android device, open a playlist and drag the songs into the order you want.
You can drag each song into place by the handle to the left of the song.
To remove songs from a playlist while using your Android device, open a playlist and touch the triangular menu button to the right of the song you want to remove, then touch Remove from playlist.
You haven't deleted this song from your device or other playlists. You removed it only from the playlist you?re working with.
Sent from my Galaxy Nexus using Android Central Forums