On your iPad, find the song you want to delete. Swipe from left to right over the song. Hit Delete.
You can also delete songs or playlists when you connect your iPad to your computer. In iTunes, select your iPad in the left column and click Music in the right column. Uncheck any music that you don't want on your iPad and click Apply or Sync.
Hope this answers your question!
Swipe your finger along the line of the song from left to right. The Delete button appears, which you can then click.
Mind you, unless you remove it from your iTunes that synced with the iPad from that particular library and its syncable selection, it will reappear the next time you hook up the iPad.
If you are still running iOS 4.3.1, IIRC you have to delete the songs by unsyncing them with iTunes, deselect (uncheck) them in iTunes while your iPad is connected to your computer and with iTunes running, and follow that with a sync.
In iOS 5 and up, you can swipe across songs in the songs tab to bring up the red delete button, or you can tap and hold down on an album icon to bring up the X to delete on the icon.