It's easy rainy when you know what to do.

When you have an internet page open for something you want to post a link to ......  look at the top of the page where you see http://www. followed by the rest of the link. 

Right click on that, which highlights it and opens a drop down menu. Click on 'copy' from that menu, then go into your reply to message in here and then right click again and choose 'paste' from the drop down menu. 

et voila!