Where are the images/characters/models that someone creates stored? Privately by the individual and/OR somewhere in Blender?
Typically, like most home computer programs, Blender stores what you create in the directory of your choice. When you press File->Save (as) or Ctrl+S to save the .blend file you'll get a File Save dialogue where you can pick where to save it and how to name it.
.blends are not stored inside the Blender App.