In case, you have turned on the Email confirmation option (double opt) in your List, you can start sending emails to your contacts upon confirmation using Automation.
You can start by creating your automated messages:
From the Automation tab -> Automated Messages – > Create Automated message.
Please check this for more information on how to create Automated messages.
Then, you can start building your workflow.
From the Automation tab -> Your Automations – > Create Automation.
Your automation should start with the Custom Event trigger followed by Send Email action.
In your trigger configuration, choose the Join List Confirmed trigger and the list you want to check for confirmation.
In the Action configuration, you can choose the email you want to send from the Automated Messages created.