what's the use of a frame , a pane or a panel in swing?

I read that JFrame is made of several panes ..what are panes and why is Jframe made of panes ? And why there is a JPanel while it seems that the JFrame looks exactly like the JPanel but with a menu bar and a close button so what's the need for a JPanel ? Can anybody explain to me clearly the definition and use of those 3 components ?