This field names the folder within which downloaded builds will be saved. Initially it will be set to the current directory when Acid is launched, but you can change it by using the Browse button (and selecting a directory from the dialog that appears) or by dragging a folder from the desktop and dropping it here.

Note that downloads are saved in subdirectories of this folder whose names reflect the camera and firmware version of the build (e.g. "CHDK/ixus70-101b").