If you're looking for reference documentation, you can consult the Nengo Modelling API documentation.
You can also dive right into the many examples that come with Nengo. These and other examples are also in the 'examples' folder of your Nengo directory.
As well, the tutorials from How to Build a Brain have been re-written for Nengo 2.0 as iPython notebooks. They will be posted shortly. If you need them, please email us.
Documentation for Nengo 1.4, can be found here: http://nengo.ca/docs/html/