How you will update a variable every time when user type into text field Which event you will use?

Details
Title | How you will update a variable every time when user type into text field Which event you will use? |
Author | Salesforce Helping Hand |
Duration | 0:41 |
File Format | MP3 / MP4 |
Original URL | https://youtube.com/watch?v=q23o6cKqN-U |