The easiest way to figure out how to do things is to find someone who's already done it, and click the edit button on their post - it'll let you see what they typed, but not change it.
To answer this question, to link to another URL:
< A HREF="http://some.url.com/blahblahblah.html"> Insert Your Description Here!< /A >
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"Illuminant light,
illuminate me."