Configuration with MailChimp

1. Add MailChimp API Key from your MailChimp account. Here is the link to get MailChimp API key - http://kb.mailchimp.com/integrations/api-integrations/about-api-keys

2. Select list for your account.

3. According to your Selected list, the merge fields will be displayed under 'woocommerce checkout fields'.

4. You can add more merge fields.

Note: These merge fields come from MailChimp List. First you have to create custom fields in MailChimp for a particular list.