There are three ways to add Kanji to the Learning List. To add the current Kanji (the one displayed in the view on the top) to your list, choose Edit->Add. To add all Kanji in the current grade to your list, choose Edit->Add All.
The current Kanji in the main Kiten window can also be added by choosing (in the main Kiten window) File->Add Kanji to Learning List.
To delete a Kanji on your Learning List, select it and choose Edit->Delete. You can also select a range of Kanji to delete by clicking in the list while holding down the Shift or Ctrl keys.