Now that there are a couple of editors open, here's how to close them.
Select the editor tab showing the first .txt file.
In the text area add a 6th line of text:
This is a 6th line
To close the editor, choose one of the following options:
Click the close button ("X") 
in the tab of the editor.
Select File > Close from the menu bar.
Note the prompt to save the file before the editor is closed.
Click OK to save any changes and close the editor.
If the editor was closed using File > Close, notice that the option File > Close All was also displayed. This is a quick way to close all of the open editors. If File > Close All is chosen, a prompt will appear to choose which editors with unsaved changes should be saved.
The preference to close editors automatically can be found in the
General > Editors
preference page. There you can configure the number of editors that can be opened prior to editors being reused and
what should occur when all editors have unsaved changes.