The top toolbar holds standard New, Open, and Save buttons on the left. If you click and hold the Save button, you will get a dropdown menu offering additional options such as Save Incremental. Next are buttons to quickly access the Render Window and 3D Preview (note that the 3D Preview button has no effect if the 3D Preview is already open, as it is in the default workspace). The rest of the toolbar contains buttons to access each of the specific UI layouts for editing the various aspects of your scene.
In a graphical user interface (GUI) on a computer a toolbar is a row, column, or block of onscreen buttons or icons that, when clicked, activate certain functions of the program.