Lists, a new feature in Twitter is a better way to organise information in Twitter. You can create both public and private lists under your profile and can add your twitter followers and also others to you list. By default the list are public, so every one can view your lists, but you can make it private. You can create any number of lists and what all lists you are creating will come under your Twitter profile/account.
For example you can create lists for your friends, business, relatives etc and make it private or public. Lists are all about segmenting your followers.
Creating lists are very simple. Click the link to know how to create lists in twitter.
Twitter users can subscribe to the lists you created.