Smart guides are intelligent guides that temporally shown while creating or moving objects (or anchor points) to allow for fast and precise alignment. They are automatically shown when Use Snapping option in enabled. What Smart guides are shown depends on what snapping options are enabled.
By default when creating/moving/resizing objects Gravit Designer will show guides to snap to any edge or center of an object. As well as the distance to nearby objects. Smart guides are also shown when equal distances between objects are reached.