When you first enter the game you will start on your Estate with Ramsey Manor as the main building along with a select few decorations. During the game you can expand your estate property by exploring locked areas. To explore another area on your estate you need to have a specific number of Trophies, Clues and Estate Coins.
Estate Plots are areas on your Estate. Some are unlocked by default, like the one with Ramsey Manor on it and some you need to unlock first.