In an IPython notebook, you write either code or text in a sequence of cells. This is a text cell.
Double click on a rendered text cell to edit it.
In [1]:
print 'here is some executable code'
The buttons along the top of the interface show you the various things you can do in the notebook. The plus button inserts a cell below the current one.
In [2]:
print 'You can execute a code cell by pressing the play button or hitting Control+Enter'
IPython notebooks are saved as .ipynb files. You can share these files directly or upload them to http://nbviewer.ipython.org/