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.