What are cells in a Notebook?
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Cells are the building block of any Jupyter notebook. Cells operate in two modes: command and edit mode and they are of  three types: 

* code
* markdown
* and Raw NBConvert

The command mode allows you to manipulate cells. This means the action you perform has to do with the cell as a whole. The command mode is indicated by a grey border around the cell with a blue indication, as shown in the below screenshot.

.. image:: ./images/install_numpy.png
    :width: 600px
    :align: center
    :alt: install numpy

When the cell is the command mode, you can perform some of the following operations: 

**INSERT --**  key in **A** to insert a new cell above, and **B** to insert a new cell below the current cell.

**MERGE existing cells -- Shift-M** allows to merge selected cells or to merge the current cell with the cell below

**COPY -- C** copies selected cells

**CUT -- X** cuts selected cells

**PASTE -- Shift-V** used to paste cells

**DELETE existing cells --** pressing **D**  deletes the current cell
 
Another mode that a Jupyter notebook cell supports is **the edit mode**. This mode specifically allows editing the content of a cell and work with it. The border around cell changes to green when the cell is in the edit mode, as shown below: 

.. image:: ./images/install_numpy.png
    :width: 600px
    :align: center
    :alt: install numpy

Once the cell is in edit mode, you can start writing code or text. The below-mentioned are some of the operations that you can perform while the cell is in the edit mode.

**COMMENTING A CODE** -- use Ctrl-/ to comment code. In markdown cells, this shortcut does not have any effect

**EXECUTE OF A CELL** -- once the code or text are written in the cell, you need to execute it. There are three primary ways to do so:

|pic1| to  run the current cell and select the next cell

|pic2| to run selected cells or the current cell

|pic3| to execute the current cell and insert the new cell below the current cell

.. |pic1| image:: ./images/shift_button.png
    :width: 20%
    :alt: shift button
    
.. |pic2| image:: ./images/ctrl_button.png
    :width: 20%
    :alt: ctrl button

.. |pic3| image:: ./images/alt_button.png
    :width: 20%
    :alt: alt button

To get a full overview of functions which are available in command and in edit mode you can open up the overview of key shortcuts by using menu entry Help → **Keyboard Shortcuts:**

.. image:: ./images/keyboard_shortcuts.png
    :width: 600px
    :align: center
    :alt: keyboard shortcuts

Notebook cells can be multiple types. Often used types are **code** and **markdown**. The code type cells allow you to write live programming code. That is, you can perform any sort of programming in them. Once you execute a code cell, Jupyter notebook will present the output just below the cell as shown in the sample  below: 

.. image:: ./images/cell.png
    :width: 600px
    :align: center
    :alt: cell

Whatever written in the markdown cell, will get printed in the cell itself, as shown below:

.. image:: ./images/cell_itself.png
    :width: 600px
    :align: center
    :alt: cell itself

As you may have noticed from the provided sample, code cells have a number associated with them, whereas markdown cells do not have any numbering. Numbering code cells helps in two ways: First, it shows the sequence in which code executed, and second, it allows us to differentiate between the code cells and markdown cells visually.