It is easy to find tutorials ( both videos and other ) for both status bar apps and popover window. Use Google to find them.
(1) Type "Cocoa Objective-C status bar app" in Google and pick a tutorial you like.
(2) Type "Cocoa Objective-C popover windows" in Google and pick a tutorial you like.
(3) Connect one of the menu items in the status bar app to the popover window. ( if you don't know how to connect menu items than best start with a Cocoa tutorial )
Both popover windows and status bar apps are Cocoa framework based and can be used by Swift or Objective-C.