How to use Ctrl + D?

To use Ctrl + D, follow these steps:

1. While you are in the terminal and have started the cat command (or any other command that accepts input), type your lines as needed.
2. When you are ready to end the input, simply press and hold the Ctrl key on your keyboard.
3. While holding Ctrl, press the D key.

This will send the EOF signal, indicating that you have finished entering data. The cat command will then process the input and return you to the command prompt.