While it would certainly be possible to simply pile all of the game code into the Game1 class, the result would be difficult to read and manage later on. Instead, we need to consider how to logically divide the game into classes that can manage themselves and help to organize our code.
A good rule of thumb is that a class should represent a single thing or type of thing. If you can say "This object is made up of these other objects" or "This object contains these objects", consider creating classes to represent those relationships.
The Flood Control game contains a game board made up of 80 pipes. We can abstract these pipes as a class called GamePiece, and provide it with the code it needs to handle rotation and provide the code that will display the piece with a Rectangle that can be used to pull the sprite off the sprite sheet.
The game board itself can be represented by a GameBoard class, which will handle managing individual GamePiece objects and be responsible...