The the easiest way to create shortlink is by using Jetpack Plugin developed by Automatic guys.
This plugin comes with a lot of modules one of them is wp.me shortlink, which will give you the ability to create shortlink for any page/post/custom post in your site.
it will be like http://wp.me/QhtyJu, but if you want to use any other shortlink service bit.ly or j.mp you can use WP Bitly
Hope this helps. 🙂