Here is a quick and easy explanation of how this works by step:

1) Click the link button (world with a link over it) and paste or enter your valid link in the box that pops up, click ok. You will see something like this:

[ URL="http:// www.flyertalk.com/"]http://www .flyertalk.com/[/URL ]

but the red part will be highlighted. * added some spaces in the link above to keep it from being parsed.

2) The highlighted part is the text of think, so just type (unless you deselected the highlighted text, in which case reselect it first and then enter the link text you desire, this will replace the red text. The link will now look like:

[ URL="http:// www.flyertalk.com/"]Some link text[/URL ]

3) There is no step three, you are all set now.