Go to Segment.com and create an account. Click this link to be taken to the signup page:
Click Settings and then click API Keys. Copy your Write Key.
Go to the Admin section in SMRT and click on Segment Integrations in Business Settings. Click Connect to Segment and paste your API key into the provided field. Click connect and you're done!
Your customer data will begin syncing with Segment. It usually takes a couple hours for all the data to sync.