The select tool is used to select various 3D elements of the reconstructed room. Elements that can be selected are pano bubbles, volumes, doors and windows. Clicking on a pano bubble will set its image as the current image, and will also move the camera to the panorama location.
To select other 3D elements, such as volumes, doors and windows, click on the desired element in the 3D viewport and it will highlight in light red.
Selecting an element, will also update the helper panel with the element's properties.