This is a bug in your code, not Python, and the error tells you how to fix it. You have to indent the block.

>>> while b < 1000:
...     print(b, end=',')
...     a, b = b, a+b

Remember to press TAB or spacebar inside indented blocks.

You should work through the tutorial.

https://docs.python.org/3/tutorial/index.html

By the way, you say page 16 of which documentation? Are you reading from a book? Which book?