I assume you mean in an HTML message. One of the icons on the menu bar at the top of the compose window, just below the Subject line, inserts bullets. Click that, enter your text, click again and enter more text and you will see the message appears in bullets. Note that the recipient sees this layout only if viewing the message in HTML view in their email client.

OK, thanks David! Put the stupidity of the question down to my being old and not especially computer-savvy! This has, of course, solved the question.

Best wishes!

It was my pleasure to assist. You're most welcome. Life is good.