First you'll need an account created in twitter.
After logging in, add a couple of entries (so when you integrate Twitter into SharePoint, you can see some updates)
Scroll down to the bottom of the page, and click on Apps
Click on Widgets
Click Continue >> at the bottom right
Select the Interactive Widget, and click Continue >>
Select the preferred style and size, then copy the code
Paste it into Content Editor Webpart on your SharePoint page