If you have not used ed, or are a casual user, you will find that the editor edit is convenient for you. It avoids some of the complexities of ex used mostly by systems programmers and persons very familiar with ed.
If you have a CRT terminal, you may wish to use a display based editor; in this case see vi(1), which is a command which focuses on the display editing portion of ex.
The Ex Reference Manual - Version 3.7 (USD:16) is a comprehensive and complete manual for the command mode features of ex, but you cannot learn to use the editor by reading it. For an introduction to more advanced forms of editing using the command mode of ex see the editing documents written by Brian Kernighan for the editor ed; the material in the introductory and advanced documents works also with ex.
An Introduction to Display Editing with Vi (USD:15) introduces the display editor vi and provides reference material on vi. In addition, the Vi Quick Reference card summarizes the commands of vi in a useful, functional way, and is useful with the Introduction.
Undo never clears the buffer modified condition.
The z command prints a number of logical rather than physical lines. More than a screen full of output may result if long lines are present.
File input/output errors don't print a name if the command line `-' option is used.
There is no easy way to do a single scan ignoring case.
The editor does not warn if text is placed in named buffers and not used before exiting the editor.
Null characters are discarded in input files, and cannot appear in resultant files.