I want to be able to send a file to my followers. How do I do this?
You can't do it directly in Twitter. You need to use a third-party app, such as TweetCube.
I think you will need to host the file in a URL and then tweet the URL to your followers
You could upload the file anywhere that has public HTTP access, and then use a URL shortener like bit.ly to create a nice tweetable link to that file location.