Richard, the URL 'Uniform Resource Locator' is just the web address, also known as the link – what appears in the address bar of your web browser when you view a page. So for your ebay item it is this:
http://www.ebay.co.uk/itm/Vertical-Alignment-Jig-/151572271639?pt=UK_Home_Garden_PowerTools_SM&hash=item234a695217
You can copy it from your web browser and paste it into the post you're composing. Let me know if you need step by step instructions for this.
It can be made into an active link by using the button which looks like a few links of chain with what is presumably meant to be a globe above it (world wide web), in the editor you use to post on this forum. It is best to just write some text first like
Vertical Alignment Jig
Then highlight it (with the mouse – hold left button down and drag over the text, then release) and click that button. Then paste the URL into the box that appears, and click OK, which gives:
Vertical Alignment Jig
The reason people are getting upset is that by not giving a link, you are forcing everyone who might be willing to answer your question helpfully to 'mess around with computers' themselves, to work out what it is you are asking about, when they too would rather be doing something more interesting.
Right or wrong, the judgement is that if you can't be bothered to do this little, easy thing to make it easier for people to answer, which it is obvious would be helpful, why should they be helpful and bother tracking down the item and answering?
Edited By Bikepete on 01/02/2015 13:30:19