Control characters are input by holding down a control key on the keyboard and simultaneously pressing a letter key or (depending on the keyboard and operating system) certain punctuation characters. Some control codes have their own special keys: escape, tab, delete, backspace, return, allowing them to be entered with a single key press.
Control characters may be output for their effect on the output device, e.g. moving the cursor or print head to the start of a new line (carriage return, Control-M), advancing down to the next line (line feed, Control-J) or ringing the bell (Control-G).
Different operating systems and application programs have different conventions for what effect typing certain control characters will have, such as interrupting the current process (Unix Control-C) or suspending or resuming output (Control-S, Control-Q).