am not able to click & drag songs to my playlists

I had a look at that reply.

'nuff said.

Personally, I would not recommend manually managing an iPod. Apart from being a cumbersome way to manage an iPod, if ever you need to Restore the iPod, or even when you simply replace it with a new one, using Sync to put the content that you had on the iPod, onto the new (or Restored) iPod, will be much easier than "manual managing"!

I have two suggestions:

1. (You may already be doing this, although the previous answer you were given has assumed that you are not:) add songs to Playlists in your iTunes Library (without the iPod connected) and then connect up the iPod and let the Sync process put those changes onto your iPod.
2. A red circle while trying to add songs to a Playlist means that iTunes cannot add the song. This may be because you are trying to add it to a Smart Playlist or to a Playlist Folder. (You can't.) You can add songs to a regular Playlist.

Smart Playlists have rules. Songs which meet those rules are automatically added to the Smart Playlists by iTunes - you cannot add any by drag-and-drop. If you wish to add a song to a Smart Playlist, either change the rules so that the song is put in (which will probably add others too) or, select the songs in the Playlist and choose New Playlist from Selection. Once you have done so, simply add the extra song.

Glad to have helped. 🙂