Simply type (or copy/paste from your browser's address bar) the long URL which you'd like to make shorter into the text box on the flit2.com main page. Click the "Shorten URL" button, and flit2.com will make the address shorter for you, and give you a new link. You can then copy your new shorter URL wherever you'd like to use it.
There is no need to visit flit2.com to use a shortened address. Simply type or paste the shortened URL into your browser's address bar and press enter, you will be automatically forwarded to the original address. If somebody has given you an flit2.com URL in the form of a hyperlink, just click on the link instead.
If you need to use flit2.com frequently, you can bookmark this 'magic' link: Shorten with flit2.com. Visiting the bookmark will then create a shortened URL for the site you are currently visiting, without you having to visit flit2.com. This functionality requires Javascript to be turned on in your browser (usually on by default), and you can safely ignore any security warnings that pop up when adding the bookmark, these are because the link contains Javascript code.