The user guide presents things regarding light, error, light sensor, and touch sensor. Inside the user guide we can get description such as controller, the touch sensor, and errors.
Lots of things like rotation sensor, input, and the rotation sensor are explained inside this user guide. These are grabbed from this user guide:
Programming LEGO NXT Robots using NXC (beta 30 or higher) (Version 2.2, June 7, 2007) by Daniele Benedettelli with revisions by John Hansen Preface As happened for good old Mindstorms RIS, CyberMaster, and Spybotics, to unleash the full power of Mindstorms NXT brick, you need a programming environment that is more handy than NXT-G, the National Instruments Labview-like graphical language that comes with NXT retail set. NXC is a programming language, invented by John Hansen, which was especially designed for the Lego robots. If you have never written a program before, don’t worry. NXC is really easy to use and this tutorial will lead you on your first steps towards it.
In addition, the user guide explains discussion such as the light sensor, sensors, and rotation sensors.