1) Launch Scripting, and go to Admin > Connectors.
2) Click the Connector Type button at the top-left, and select Twitter from the list.
3) Click the button to add a new Connector.
4) Add an appropriate name - Twitter connectors are split into Mentions and Messages, so it's worth naming the Connector appropriately.
5) Enter the account's @username, Consumer Key and Consumer Secret, and Access Token and Access Token Secret. Select the desired interaction type from the Data Feed drop down at the bottom.
6) Click Save, and repeat for any other desired interaction types or pages.