The current data folder is the default directory for reading or storing data by functions such as ReadTextFile(), WriteTextFile(), and SpreadsheetOpen(). If you specify relative paths as parameters to these functions, they interpret them as relatvie to this folder.
With no parameters, CurrentDataFolder(), returns the full path for the current data directory.
With one parameter, CurrentDataFolder(«directoryPath»), sets the current data folder to «directoryPath», which may be relative to the current folder or a full path. Given a valid path, it returns the new full path to the current data folder.
If you change the folder in an open or save file dialog from a file read or write function, it will change the current data folder.
There is also a current model folder, accessed with CurrentModelFolder(), that is the default directory for saving and loading models and modules. When you start a model, CurrentDataFolder is set, by default, to the current model folder. But the current data and model folders may change separately thereafter.