Sealtm2, there are three different ways to get working URLs, if neither works for you (and you're sure you're doing it right), then your browser might be the problem, or a bug in rosity's forum code in failing to deal properly with your browser.

1. if you only have one URL to share, you can put it in the long text fields below the reply input itself, where it says Link Name & Url.  the URL goes in the bottom (make sure you only have one "http://" at the start), the text you want for it in the top -- you can also leave that empty, then the URL itself will be the text).  this one has worked for me in all browsers i've tried.

2. if you want to share more than one URL, and if your browser shows two rows of icons and dropdown menus directly above the reply input, type the text for the URL (or paste the URL itself if you don't care about the text), highlight it, and click the tiny earth with a chainlink in the 2nd row.  a dialogue box will appear, where you can paste the URL.  click ok, and watch as the link appears in your reply input.  this does not work in all browsers, though if it doesn't work, you shouldn't even get those top two rows.  for example opera doesn't do it.

3. in those browsers where option 2 doesn't work (i tested this in opera), you can use standard html to insert a link: text on which to click.

disclaimer:  this is how things were last week.  they might have changed.  if you can't get anything to work, i suggest to report it in the community forum, it's possibly a bug.