While not entering text you use vi in command mode and enter editing commands consisting of one or more characters.
The syntax of an editing command is:
The operator is a character -such as d for delete- that describes the action to be carried out on the object; a word, sentence, paragraph or section.
To return to command mode from insert mode press the ESC key. If you are already in command mode the terminal will beep at you (or make some similar sound).