I hope this will help people who are trying to use WordPress for the first time, and want to know how to create a link to an external site, or an email address, from scratch. It is not that difficult, but some people (me for instance) can get confused!
A link consists of three things:-
1) the address of a website itself, prefixed by http:// (or if it is an email address, mailto://)
2) The text that appears on the page underlined in green, or it may be a button, which takes you to the link when clicked; and
3) the optional text that appears when you mouse over the link.
The easiest way to create a link on this site is first to copy the link to the clipboard; then write the text that you want to appear on the page; highlight it and press the link button; then paste the link into the first window that appears (the one with http:// already highlighted).
The second window below that is for specifying whether the link should appear in the same or a new window; and there are other options as well.
If anything goes wrong, just highlight the link and click the Unlink button to the right of the Link button.