I can never remember how to do this, but Stu's Help thread is full of them so here's an example (which I can grab by editing his post)
For lots more info please check out the Club Arnage main site
here.So, start the sentence
For lots more info please check out the Club Arnage main site
then (square bracket)url=http://(your URL name e.g.
www.clubarnage.comthen] and the text you want to appear as the link (in the example this is "here."
Then [/url] at the end
I'll mail you this example, to clarify.
Not all forums use the same characters, and some disable this functionality. I use a forum where is is the < > instead of the [ ].