It's quite simple, really. When you click the "http://" tag above the post you're typing, it asks you to enter two things. The first is the website address (which you seem to already understand) and it has to be a website address. The second thing it asks for is what the link in your post should say. In your case, you've simply copied the web address again, when in fact you can type in anything you want. I hope that made sense to you.