To connect your Twitter account, login to Resurface and navigate to the "Social Profiles" page. The link to it will be on the navigation menu at the top.
Click on the "Connect" button next to the Twitter icon, when you do this, you'll see this window popup:
If you're not logged into your Twitter account, then login using your Twitter username and password. If you're already logged in, you'll just need to grant Resurface access to your account.
Once you've done this, your Twitter account will be listed as a connected social media profile.
That's it! You've successfully connected your Twitter account to Resurface, and you'll be able to schedule tweets.