The whole GiD manual is splitted in 3 volumes: Reference, User and Customization manuals.
In this volume, Reference Manual, there is a first part devoted to general aspects, which provides information on the basic aspects of the program. In this way, you can gain confidence and become more familiar with the system in order to take advantage of all the available facilities.
Then you can find detailed information of all the features of GiD following the structure of the menus (both in preprocessing and postprocessing part of GiD).
The User Manual volume contains a collection of tutorials and practical information for learning the basics and advanced features of GiD, covering full flow of GiD user from preprocessing to postprocessing going trough meshing, analysis and introduction to customization.
The last volume, Customization Manual, its adressed basically to developers of modules, and explains how to customize your files so that you can introduce and run different solver modules from GiD according to your own requirements. The way of customizeing graphical interface and behaviour of GiD as users needs is also explained in this manual.