There are two different working modes for the Jupyter Notebook.
Therefore , the same keyboard key press has different effect, depending on which mode the notebook is in currently.
There are two modes:
When in edit mode of jupyter notebook, you can type code and text. we can enter this mode, by pressing enter or clicking the mouse on a cell editor area. Edit mode is identified by a green cell border.
With Jupyter notebook command mode, we can edit the complete notebook but not the individual cells. we can enter the command mode of jupyter notebook , by pressing escape or clicking the mouse outside a cell.
For example a command mode operation could be pressing the c letter on the keyboard, that will copy the current selected cell.
You may like to watch this video, for more information about edit mode and command mode of jupyter notebook alsong with the Jupyter Notebook Intellisense and autocomplete feature with Menu Shortcuts.