View > Windows > Book
The Book Window shows the book moves of the current position in the game.
If the window is empty choose Book > Open to open a book.
At the top left is N=603139, which is the number of games in which the current position has occurred.
To the right of it is the winning percentage of the current position.
Move
Actual moves played are black and bold. Sometimes a move is gray. A gray move is never played, but leads to a position that results from some other line (tranpositions). Sometimes a move is black but not bold: this is the last move played (retro moves).
Games
Shows the number of games with the position after the move is executed.
Percentage
Shows the percentage score of the position after the move is executed. The percentage is always from the point of view of the color to play. To calculate the percentage, half the number of draws are added to the won games.
Statistics
At the bottom of the window you see the statistics. The number of games of the selected move is split up in the number of won games, the number of lost games and the number of draws.
When you double-click a move, or press Enter, it is added to the notation of the game. You can use arrow-up and arrow-down to select a move.