If so write want you a want to say, then highlight the words, click the chain icon and copy the link to the page you want into the box that appears. Press ok and you should be set.
Keep in mind this forum software defaults to a rich text editor, but under the hood, it's using markup that's the same as other messageboards you've probably used (vBulletin, etc.)
So while there's the solution as provided above, you can toggle the Rich Editor off, and switch to BB mode using the wrench icon on the top, right of the text input.
Then you'll see the underlying code:
Code:
[URL='http://www.google.com']Link[/URL]
Which is typical BB code.
If you use that even in Rich Text mode it will still get parsed correctly (entering the same BB code below, Rich Text mode, after posting or previewing it will be converted):
If so write want you a want to say, then highlight the words, click the chain icon and copy the link to the page you want into the box that appears. Press ok and you should be set.