save how to get back to the old stage of the game (The Witcher 3: Wild Hunt)

Prompt, please, where are stored the save files of the game, what is their extension? Is there a possibility to sign to conserve so then to be guided by their names? Because the inability to replay a long time - now the only thing that is really confusing in this masterpiece game. From the download menu of the game available only the most recent save, and a few old randomly selected game