Tweets have shortened URLs. RSS feeds have URLs which points to ads or counters. However, the original long URL is more informative and is easier to remember.
This tool is to expand (lengthen) URLs in shared text which you send from your Twitter or RSS reader application to email, chat, etc. You should just pass the text through the "lengthener".
When you share a text with links, do it through this app (choose "URL Lengthener" from the list of share target). The app searches URLs in the shared text and replaces them with longer versions and then shares the modified text again. So then the share targets list appears again, choose the actual target now. Note the app requires Internet access, otherwise URLs stay unmodified.