A hint for your next move is shown. Only possible if you play at level normal or above, the move number is 2 or greater and you have not undone your move.
When the computer is thinking, his depth search is interrupted and he draws the best move he has found so far.
Take back your previous move. Two (!) moves are undone: the opponents move and your last move. So it's your turn again. 100 moves are remembered; so don't hesitate to take back moves until you are at the beginning of the game (faster with the F2 key). When in Modify mode (see -> below), decrement move number of this position.
Only useful in Modify mode: Increment move number of this position.