First off, I believe that in this site's rules, posting of a current auction's live link is not permitted in certain forums....???
Also, be aware of copyright laws, forum copyright rules, plus, the Digital Millenium Copyright Act.
To place a link within Your post, click on Go Advanced: The button is to the lower right of the reply box.
FWIW: This step is not actually a neccessity, but will allow You to preview Your post, then test the link You've posted.
Highlight the link that You'd care to post, on Your keyboard hit ctrl and the letter C, take the link to the forum boards, and click on what appears to be a planet, just above the posting box.
You will see a space to paste Your link into; do so by clicking on that space, then hit ctrl V on You keyboard, and preview the post, submit reply when satisfied.
Another method:
Place brackets [ ] with url typed inside before Your link, and [/url] aft of Your link, then click Preview Post, and submit reply.
Hope this helps!