Toolbars are bars on top of most program windows represented with icons and/or text. They are shortcuts to functions which are usually available from other places like Main Menu and clicking on toolbar icon will trigger associated Main Menu function.
Some toolbar icons have a submenu. The menu can be displayed by clicking arrow down next to a button. The menu may offer more options related to that particular button. For example, Send and Receive button on the main toolbar also has a menu with additional actions - Send and Receive All, Receive All and Send All.