What are the costs involved for the end user? Is it free? If so, tell them.
Consider your filter tweets section from an adoption standpoint:
Create filters to automatically move Tweets to folders, and reduce Twitter noise. Tweets can be filtered based on hashtags, URLs, Tweet content and author - or any combination of these.
1. I wouldn't recommend using the name 'folders'. Tweets aren't synonymous with letters (that go into folders), tweets are more like sticky notes. I'd suggest you think of a new name to call the tweet containers.
2. You first talk about moving tweets into folders and then about filtering them. (I think you are implying that you filter tweets into these 'folders'). You should use easier to understand terms such as 'Sort tweets from those who you are following into ...'. Use comparisons to simplify the explanation.
3. Provide sensible defaults or provide a sensible way to get users started. (ex. type in the twitter handle/username from your favourite tweeter). A demo is a good idea, but there should definitely also be an easy way to get started.
4. Market yourself effectively. From what I see on your website, it seems like the website is a twitter client - but I'm not sure. If it is a client, then say so. (You have to tell people what you want them to use your service for).
Some of the above recommendations simply require rewriting your copy (text on website). I have also suggested some options that will require hiring a developer. I reckon the best measure to use here is: if your mother uses twitter, will you be able to sit her down and will she be a 'self-starter' using your website or will you have to hold her hand? Try it. She'll definitely give you some useful input.:)