There are various reasons why you might want to shorten the HUGE urls that lots of web pages have.
You might want to write it up on the board, use it on Twitter ( where you have really limited space to type ), write it on a document so it doesn't look long and messy....... etc.
Here is one way to do that using the Google url shortener.
There are other URL shorteners in the useful links section at the bottom of the page.
Ow.ly - Shortener to use on twitter. This also tracks the views.