Go to the https://mailchimp.com/ and create a MailChimp account. Now create a Embedded form.

1. Click Audience, then choose Signup forms.
2. Click Create new form.
3. Click Create embedded form.
4. Enter a name for your form, then click the Audience drop-down to choose the audience you want to work with.
5. Click Continue to builder.

Add your MailChimp post URL