Mailchimp is an email marketing software that allows users to create email campaigns and lists. It has drag and drop functionality for designing emails and built-in tools for embedding opt-in forms on websites. The tutorial walks through signing up for a free Mailchimp account, creating an email list by importing contacts, designing opt-in and thank you forms, building an email template, and sending a test campaign to the list. It also covers integrations and accessing the API key to connect Mailchimp with other applications.