Expansion packs and worlds..

if you had a save game with your sim then that save should have been on the main menu to load that save game to carry on playing in say if you where in sunset valley you click on that save game in your menu to start playing from build/buy mode you can use the content from the other packs to use in your home world i.e.  in sunset valley

the expansions and or stuff packs combines with your base game for playing the game will launch from your newest installed released game to play

store worlds once bought/downloaded/installed will be in the maim menu +new game to select the store bought world to play in BUT the game will play from whatever game you normally load up from

for worlds that come with an EP  for example moonlit falls that too will be in the main menu to select the world to play in with any sim you have saved in your libiary