ed is only capable of editing one file at a time. Follow the next example to create your first text file using ed.
/home/larry# ed a This is my first text file using ed. This is really fun. . w firstone.txt /home/larry# q
You can verify the file's contents using the Unix concatenate utility.
/home/larry# cat firstone.txt
The above example has illustrated a number of important points. When invoking ed as above you will have an empty file. The key [a] is used to add text to the file. To end the text entering session, a period [.] is used in the first column of the text. To save the text to a file, the key [q] is used in combination with the file's name and finally, the key [q] is used to exit the editor.
The most important observation is the two modes of operation. Initially the editor is in command mode. A command is defined by characters, so to ascertain what the user's intention is, ed uses a text mode, and a command mode.