Markdown cells are used for documentation purposes.
The text can be marked up with the Markdown language, which provides a simple way to define which part of the text should be emphasized (italics), bold, form lists, etc.
Markdown also allows arbitrary HTML code for formatting.
Within Markdown cells, you can also include mathematics, using standard LaTeX notation: $...$ for inline mathematics and $$...$$ for displayed mathematics.
Standard mathematics environments defined by LaTeX and AMS-LaTeX also work, such as \begin{equation}...\end{equation}, and \begin{align}...\end{align}.
New LaTeX macros may be defined using standard methods, such as \newcommand, by placing them anywhere between math delimiters in a Markdown cell. These definitions are then available throughout the rest of the IPython session.
Raw cells provide a place in which you can write output directly. Raw cells are not evaluated by the notebook. When passed through nbconvert, raw cells arrive in the destination format unmodified.