The Toolbar is the section located at the top of the editor window. It contains menu buttons that give you access to various functions of CKEditor. All buttons are grouped according to their function and include both simple operations (like basic text styling or formatting) and more advanced features (like inserting media or forms via a dialog window).
This is what the editor toolbar looks like:
The CKEditor toolbar buttons are illustrated with meaningful icons. If, however, you are not sure what functions they perform, hover the mouse cursor over the buttons to see a tooltip with the name of the function.
In order to perform an operation assigned to a button, click the button once. In most cases it will either immediately perform some predefined action or open a dialog window with further configuration options for a feature.
Some of the buttons serve as placeholders giving you access to further options placed in a drop-down list. They are easily recognizable thanks to a small 
icon on their right. Clicking the name or the arrow icon of such button expands the list and lets you choose one of its options via the left mouse button. To select a drop-down list option you can also use the Tab or the Down Arrow key and then accept your choice by pressing Enter or Space on your keyboard. To hide the list, use the Esc key or click anywhere in the browser window.
To save on screen estate, you can collapse the toolbar by pressing the 
button or using the Alt+- (minus) keyboard shortcut. In order to return to the full toolbar view, press the same button or keyboard shortcut again.