Undo the last move. If the previous player is played by the computer two moves are taken back so that it is the player's turn again.

Replay a move which had been undone. If one of the players is played by the computer two moves are redone so that it is the player's turn again.

The computer will calculate the best possible move for you and mark it with a sign on the game board. How good the move actually is depends on the level of the computer.