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 Settings -> Business Settings -> Segment Integration section in SMRT. 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.