ToutApp uses the Contact or Lead ID (also known as Salesforce ID), to help log information properly to Salesforce. There are a few ways that you can attach your Salesforce ID to your contacts in ToutApp.
1) Push to Tout: Using Push to Tout will create a contact in ToutApp with all the key contact information including the lead/contact's Salesforce ID.
2) Email with Tout: When you use Email with Tout from Salesforce a contact will be created in ToutApp with a Salesforce ID associated with it.
3) Import CSV: If you export a list of leads/contacts from Salesforce and you include a column with the Salesforce ID then you can map the field to ToutApp on import.