On graphical displays, Emacs puts a tool bar at the top of each frame, just below the menu bar. This is a row of icons which you can click on with the mouse to invoke various commands.
The global (default) tool bar contains general commands. Some major modes define their own tool bars; whenever a buffer with such a major mode is current, the mode's tool bar replaces the global tool bar.
To toggle the use of tool bars, type M-x tool-bar-mode. This
command applies to all frames, including frames yet to be created. To
control the use of tool bars at startup, customize the variable
When Emacs is compiled with GTK+ support, each tool bar item can
consist of an image, or a text label, or both. By default, Emacs
follows the Gnome desktop's tool bar style setting; if none is
defined, it displays tool bar items as just images. To impose a
specific tool bar style, customize the variable
You can also control the placement of the tool bar for the GTK+ tool
bar with the frame parameter
tool-bar-position. See Frame Parameters.
NS builds consider the tool bar to be a window decoration, and therefore do not display it when a window is undecorated. See Frame Parameters. On macOS the tool bar is hidden when the frame is put into fullscreen, but can be displayed by moving the mouse pointer to the top of the screen.