To link a Twitter account for auto-tweeting new events and articles from your SilkStart site, navigate to Settings > Social Integration in your admin panel.
Click the button to Sign in with Twitter.
If you'd like to auto-tweet your calendar events, navigate to Settings > Apps > Events in your admin panel and uncheck the box that says "Suppress Event Notifications". What this will do is send a notification to admins when a new event is posted, plus let you choose to tweet about an event when you create it.
When you are creating your event, expand the Advanced Options section and check the box for "Autotweet this event" - this will send a tweet when you event is created.