EnSight has a large and detailed documentation, that gets updated at each major new release.
There are a number of different Manuals; each of them aims at a different kind of user:
The Getting Started Manual is intended to help new users get a feeling of how EnSight works, guiding the user step by step in some of the most common analysis
The How To Manual is a guide to the Interactive EnSight. For each of the analysis you may want to perform, it shows the interactive window and explains the available options.
The User Manual is a Manual for the intermediate user. All the feature of EnSight are here explained in more detail, giving e.g. a little algorithmic overview and formatting information for read-in files. A detailed list of the defined functions of the Calculator can be found here.
The Interface Manual, finally, is the manual for the advanced users, who are willing to write small codes to personalize the analysis that EnSight can perform.
All these manuals can be found when you open EnSight, in the Help menu. They can also be found in your directory: