Gone are the days when you has to shorten a link first before you could add it your tweet.
Now when you post the normal link to tweet box twitter will automatically shorten it using it own url shortner t.co
The shortened URL will be 19 characters long. Twitter will also show a shortened version of the original link, so that people will know which site the link points to. This is aimed at increasing security.
But you will not be able to get link analytics though for which you can use services like Hootsuite.