Visitors do not automatically receive an email from you once they sign up for your mailing list unless you are a PRO user and you enable one (or both) of the following mechanisms.
If you set up a Reader Magnet in Content > Email Signup, visitors who sign up will receive a standard email immediately with the bonus content you uploaded there.
If you set up a Welcome Email in Marketing > Email Campaigns > Automations, visitors who sign up will receive a personalized message from you automatically. Turn on the switch for the Welcome Email and click 'Edit Welcome Email' to customize.