Getting the direct Twitter link is easy, but I admit it had me stymied for a while too before I figured it out. :)
After you've posted your tweet, when it then shows up underneath the blank box, there will be a "time stamp" on it underneath what you just tweeted, for example "5 seconds ago" or whatever.
If you click on that time stamp, it will open just that tweet in a new window. You then copy the URL address from the address bar in your browser and that is your direct tweet link.
I found a shortcut to that, though. Instead of clicking on the time stamp and opening it in a new window, you can simply right click on the time stamp and "copy shortcut" (for Firefox users, it is "copy link location"). That also puts the tweet link on your clipboard just like copying it from the URL bar in your browser.
Try it! :)