If you want to collecting leads with MailChimp, here is a quick guide:

Open your project in the editor and select a block with the ability to collect data (lead form, for example). Then, click Edit:

Scroll down and you will see a MailChimp in Integrations section. Click Set up button:

You will see an authorization page. Enter your username and password of Mailchimp and click Log In:

Allow access to your account, by clicking Allow:

Perform field mapping and click Test & Save:

It's done! Everything is ready for data collection!