The Status Bar is used, as in many applications, to give the user cues about the current state of the application, information about selected items in the GUI, and various error/warning messages that don't result in a dialog requiring user intervention.
Under normal conditions, the Status Bar will say "Ready", indicating that MIB Smithy is waiting for user activity. If the application is busy, such as when saving a MIB file, the Status Bar may indicate what MIB Smithy is currently doing.
Figure - MIB Smithy Status Bar
For many items in the MIB Smithy GUI, such as buttons on the toolbar, placing the mouse cursor over the item will change the Status Bar message to indicate what the item is used for. For instance, placing the mouse cursor over the Add Module button changes the Status Bar message to "Add Module", indicating that the button is used to create a new MIB Module within the selected file/project.