If you're on the page you want to link to, go up to the address bar. Select or highlight the address, right click and select copy.
When you're back here, replying, right click and select paste. Press "enter" and it will turn into a live link when you post your reply.
Right now, my address bar shows Splitcoaststampers.com; when I click on it, it turns blue and allows me to copy it.
One of those things that are so easy once you know how!