Mailchimp is a leading marketing automation platform and email marketing platform for small businesses and personal use, mostly used for Webflow and no code enhusiasts for building audience and sending newsletters to subscribers.
You can start by creating new Audience list or importing your existing subscribers from other platforms for free. This plan includes 2000 contacts, 10000 emails sent per month and limit of 2000 per day. Free plan includes access to some basic Mailchimp Templates, but for more you will have to subscribe to next, Essential plan which costs $9.99/month and includes 3 seats instead of just one.
Apart from those basic features, you can check detailed analysis of their feature on Mailchimp 101 page.