The mouse has (at least) two buttons that are used in different manners. The left button selects/deselects and accesses items such as geometry, bodies, text boxes, buttons, etc.The right button will access context menus which contain items specific to the selected objects. Right-click a title bar of certain dialogs to open a menu containing items specific to that dialog.
An example of a context menu is shown to the right. Right-click 
the History list title bar to see its context menu. The menu only contains options that are applicable to the History list.
