The Player Information window is produced or updated whenever you click the left mouse button on a player name in the game information area (below the chessboard) or in the crosstable window.
It displays (hopefully) useful information about the player, including their success with White and Black, favorite openings (by ECO code), and rating history.
All percentages displayed are an expected score (success rate), from the player's perspective -- so higher is always better for the player, whether they are White or Black.
You can see the player's rating history in a graph by pressing the Rating graph button.
Any number printed in red can be clicked with the left mouse button to set the filter to the games it represents.