At twitter you can post upto 140 charactes in your message. Yiou can post or say tweet what you are currently doing, your thought etc at twitter and same will be passed on to all your followers.
Here are few steps through which you can increase your email list with twitter:
1 – Brand your twitter username instead of just using any generic name.
2 – Have your detailed info in twitter bio field.
3 – Have a freebie to give away. You may want to create a unique electronic giveaway just for your Twitter followers, or you can use the same giveaway that you already use on your site. Once you’ve decided what to give away, create a squeeze page and insert sales copy and an opt-in form so that you can direct your Twitter followers to this page for them to join your list and receive your free giveaway. For tracking purposes, you may want to set up a unique page to see just how many subscribers join your list from this invitation.