Compared to Notepad, TextEdit is far more fully-featured. We have to deliberately “dumb it down” in order to work to our purposes.
First, run TextEdit. You can find it under System / Applications / TextEdit in most installations of OS X. (Ensure that you are running TextEdit 1.7 or higher: 1.6 has a bug in saving .html files)
You will find that by default TextEdit appears as a simplified word processor, with rulers, margins, tab indents, alignment control, etc. For our purposes, we want to make sure that TextEdit starts a new document without these features.
In the menu bar of TextEdit, go to File / Preferences. (Alternatively, and faster: Press Command-,. That is the shortcut to preferences in most OS X applications, with a few exceptions).
In the Preferences dialog, under the New Document option, change the settings to what is shown in the image to the right. (Note that the plain text font setting shown may be a little large for your purpose – feel free to change the font and size to whatever you find the most legible).
Then, under the Open and Save option of the Preferences pane for TextEdit, change the settings to what you see to the right:
Close the Preferences pane (fastest method: Command-W).
Note that the current document is unchanged. You have changed preferences for future documents written in TextEdit, but not the currently open one. Close the current document (again, fastest option: Command-W, which always closes the active window).
Create a new document (fastest method: Command-N). It should be a blank page, free of rulers, alignment controls and other features.